Effects of time zones on North American broadcasting

The scheduling of television programming in North America (namely the United States, Canada, Mexico and Greenland) must cope with eighteen time zones. The United States (excluding territories) has six time zones (Hawaii-Aleutian, Alaska, Pacific, Mountain, Central and Eastern), with further variation in the observance of daylight saving time. Canada also has six time zones (Pacific, Mountain, Central, Eastern, Atlantic and Newfoundland). Mexico has four time zones (Pacific, Mountain, Central, and Eastern). Greenland has three (Atlantic time, UTC−03 and UTC−01, with UTC−02 not used). This requires broadcast and pay television networks in each country to shift programs in time to show them in different regions.

Canada

Broadcast networks

Canadian broadcasting networks, with six time zones and a much larger percentage of its audience residing in the Mountain Time Zone than in the Central Time Zone, are sometimes able to avoid the issues that affect American programming by airing pre-recorded programs on local time. CBC Television and CTV created delay centres in Calgary in the early 1960s in order to allow programming to air in each time zone based on the region. Newfoundland and Labrador pose a problem which cannot be addressed by delaying content, as most of the province uses a Newfoundland Time Zone one half-hour ahead of the nearby Maritimes region. Saskatchewan poses scheduling issues as most of the province does not observe daylight saving time, remaining on Central Standard Time year-round. While clocks in most of Saskatchewan match those in Winnipeg during the winter, they match clocks in Calgary and Edmonton during the summer, despite the fact that Alberta is in the Mountain Time Zone. Schedules must therefore be adjusted during the summer in some areas. The exception to this rule is Lloydminster, which straddles the Alberta/Saskatchewan border; it is on Mountain Time year-round.

In the vast majority of cases, local time schedules on CBC Television stations (and, for that matter, the CBC's radio networks) are identical in all markets, except for certain types of live programming and the aforementioned oddity of the Newfoundland Time Zone; CBC stations in Newfoundland use the same network feeds as the Maritimes so programs are scheduled for 30 minutes "later" than other parts of the country, typically noted in the CBC's network promotions with phrasing such as "6 o'clock, 6:30 in Newfoundland." Since the majority of Labrador is in the Atlantic Time Zone, whenever the province's two full-fledged stations, CJON and CBNT (both based in St. John's), originate local programming, they usually refer to it as "coming up at 6 o'clock, 5:30 in most of Labrador." On the French-language Radio-Canada network, use of the phrase « "une heure plus tard dans les Maritimes" is as commonplace on programming which transmitted live in Montréal, as "half an hour later in Newfoundland" is on English-language CBC programming which transmitted live in Halifax.

However, particularly among private broadcasters, there are often significant variances in local schedules from one time zone to the next due to the preference for showing American programs at the same time as the American network affiliates available through local cable and satellite television providers, which maintains a Canadian broadcaster's access to simultaneous substitution. This is further complicated by the fact that the affiliates available are not necessarily from the same time zone. For example, the easternmost time zone in the United States is the Eastern Time Zone, so viewers in Atlantic Canada always receive American network affiliates from that time zone. Meanwhile, while Calgary and Edmonton are on Mountain Time, the American stations available in Alberta have always come from Spokane, Washington; which is in the Pacific Time Zone. This is likely because Spokane was the nearest market to Alberta that had full service from the Big Three networks in the 1950s; although Alberta borders Montana, much of that state did not receive full network service until the 1980s. Hence in both the Atlantic and Mountain time zones, American "prime time" actually runs from 9:00 p.m. to midnight.

Accordingly, while private Canadian networks have generally adopted the American practice of broadcasting simultaneously to the Eastern and Central time zones ("8:00, 7:00 Central"), in recent years they have standardized on a different approach for stations in the Atlantic and Mountain time zones. In these markets, American programming is simulcast between 9:00 and 11:00 p.m. local time (8:00 to 10:00 on the American stations being simsubbed), while the American "10:00 p.m." program, despite often being dramatically darker or more adult in tone, is usually telecast earlier in the evening at 8:00 p.m. local time. In the case of lengthy events such as movies or awards shows which extend into the 10:00 p.m. Eastern and Pacific Time hour, the program will usually be scheduled to air within the local primetime block if possible (although surrendering any local simsub privileges for that program in the process) or simply aired to its conclusion in the case of live events (particularly in the Atlantic time zone). In Newfoundland, the lone local private station, CJON-DT, currently follows the lead of its Maritime counterparts in most cases, but again with a further 30-minute "delay" for Newfoundland Time. Similar abnormalities occur in Saskatchewan; both CTV and Global's affiliates in Saskatchewan follow similar scheduling patterns to their Winnipeg affiliates year-round (running primetime from 7:00 to 10:00 p.m.), but enact a one-hour delay on programming once daylight saving time takes effect in order to maintain continuity in scheduling.

A small number of Canadian television networks are not broadcast to a national audience such as over-the-air networks CTV Two and City – which are broadcast only in certain markets and which do not have any stations in the Yukon Territory, Nunavut or the Northwest Territories. Such channels may not require significant timeshifting, since they only cover a few time zones instead of serving all six time zones that serve the country. Ici Radio-Canada Télé, the French counterpart of CBC Television, has four feeds to allow programs to air at the same time in each zone's local time, except for the Atlantic and Newfoundland time zones, which telecast programs at the same time as in the Eastern Time zone, but 60 and 90 minutes later respectively on their clocks (e.g. 20h00 HE/21h00 HA/21h30 HT).

Cable and satellite channels

The vast majority of specialty cable and satellite television channels in Canada each operate a single feed which is distributed in all time zones. This includes all French language channels, as they predominantly serve Francophone areas of the country, mostly in Quebec (almost all of which observes Eastern Time). Even many long-standing specialty channels with a general-entertainment orientation, such as Showcase and Bravo, use a single national feed, though in many cases they will repeat core primetime programming three hours after first broadcast, such that programs can be promoted as airing at the same time in both the Eastern and Pacific time zones.

Some specialty channels, including YTV, Teletoon and The Comedy Network, do operate two separate broadcast feeds for Eastern and Western Canada. The Eastern feed airs programs on an Eastern Time schedule, while the Western feed airs the same programming three hours later on Pacific Time. The separation between feeds is typically implemented at the border between Manitoba and Ontario, which may result in a program that airs at 10:00 p.m. Eastern Time in Ontario not airing in Manitoba until 12:00 a.m. Central Time (whereas an equivalent program in the U.S. would typically be available at 9:00 p.m. for Central Time viewers). However, one channel, the Aboriginal Peoples Television Network, implements the separation at the border between Manitoba and Saskatchewan.

Premium cable channels Movie Central and The Movie Network broadcast in separate areas of Canada (Movie Central in the Territories and Western Canada, and The Movie Network in Ontario, Quebec and the Atlantic Provinces), and therefore programming on both services can be scheduled only with regards to the few time zones within each service's territory. However, unlike most "western" specialty channel feeds, Movie Central (which was originally based in Alberta) uses Mountain Time as its primary time zone. As a result, the West Coast feed of HBO Canada (which is jointly managed by Movie Central and The Movie Network's respective corporate parents, Corus Entertainment and Bell Media) airs programming only two hours after the East feed, and accordingly programs are promoted as airing at (for example) "9pm ET/MT".

Sports broadcasters including TSN and Sportsnet operate multiple channels, some of which have been designated as "primary" feeds for a specific region of Canada. However the main motivation for these feeds is to allow for broadcasts of multiple live events, including events of specific local interest or broadcast availability, regardless of the primary time zone(s) served by each feed. Nonetheless, there is occasionally timeshifting of studio and/or pre-recorded programming between these feeds.

Watershed and safe harbour

The Canadian Broadcast Standards Council (CBSC) applies more restrictive censorship regulations to broadcast programming shown in prime time, compared to content transmitted after a watershed hour beyond which few children would be likely to be watching. This can be problematic if the same content is broadcast simultaneously nationwide, as the 9:00 p.m. watershed in Vancouver falls at 12:00 a.m. in Toronto and 1:30 a.m. in St. John's. LGBT specialty broadcaster PrideVision (before its split as OutTV) was particularly affected as, from its launch in 2001 until 2005, its format included more innocuous entertainment programming aimed at the gay community during the day and in prime time and hardcore pornographic content in the overnight (with the latter expanding into the mid-evening by 2004).

Greenland

The UTC−03:00 Standard Time Zone is commonly used as a de facto official time by the Greenlander main broadcasting station Kalaallit Nunaata Radioa; there are three time zones but most of the island's population resides in the UTC−03:00 zone, which covers the central one-third of Greenland. Thus broadcasters sometimes avoid timeshifting issues by airing programs on UTC-03:00 time. This is a problem in the eastern town of Ittoqqortoormiit as the settlement and its surrounding area uses UTC−01:00 Standard Time Zone. Both time zones observe daylight saving time with European Union DST rules.

The UTC−04:00 Standard Time Zone is used in northwestern Greenland, and the area around Thule Air Base observes North American daylight saving time rules, known in Canada as the Atlantic Time Zone and in the Caribbean as the "Eastern Caribbean Time Zone". The UTC−02:00 Standard Time Zone is not used.

Mexico

The Central Time Zone is commonly used as a sort of de facto official time for the Mexican broadcasting networks, with three time zones to span. Since a much larger percentage of its audience resides in the Central Time Zone than in the Mountain Time Zone, stations often broadcast their programs on Central Time. This is particularly a problem in Sonora since the whole state does not observe daylight saving time and remains on Mountain Standard Time year-round (this matches the practice of Arizona, with which it shares a long border). The thinly-populated Revillagigedo Islands also do not observe daylight saving time and remains on Mountain Standard Time year-round, with the minor exception of Clarion Island, which remains on Pacific Standard Time year-round.

When the American government extended its daylight time period in 2007, Mexico did not change its effective dates. This means that in most of the country, daylight saving time starts three or four weeks later and ends one week earlier than in the United States and Canada. However, border cities in Tamaulipas, Nuevo Leon, Coahuila, Chihuahua and Baja California observe the same daylight saving time period as the United States to avoid cross-border confusion.

During the period when the United States and Canada are on daylight saving time and most of Mexico is not:

• Tijuana and Mexicali are one hour behind Mexico City;
• The northern border cities of Chihuahua have the same time as Mexico City;
• Northern border cities in Coahuila, Nuevo León and Tamaulipas are one hour ahead of Mexico City.

United States

Time zone feeds

With four time zones in the contiguous United States, American broadcast television networks generally broadcast at least two separate feeds to their owned-and-operated stations and affiliates, as do cable/satellite channels: the "eastern feed" that is aired simultaneously in the Eastern and Central Time Zones, and the "western feed" that is tape-delayed three hours for those in the Pacific Time Zone. This ensures that a program, for example, that airs at 8:00 p.m. on the East Coast is also shown locally at 8:00 p.m. on the West Coast. Networks may also broadcast a third feed specifically for the Mountain Time Zone, on which programs are usually broadcast on a one-hour delay from the Eastern Time Zone. Otherwise, some stations in the Mountain Time Zone use the western feed, while others get a mix of both the Eastern and Pacific feeds.

The Eastern Time Zone is commonly used as a de facto official time for the United States – since it includes the nation's capital city, Washington, D.C.; the country's largest city, New York City; and about one-half of the country's population. Because of this, television schedules are almost always posted in Eastern Time. Broadcast networks and cable channels also advertise airtimes in Eastern Time, often also including either the Central or Pacific Time Zone. This has led to conventions like "tonight at 9:00/8:00 Central" (referring to the eastern feed), "tonight at 9:00 p.m. Eastern and Pacific" (referring to both the eastern feed and the three-hour delayed western feed) and "tonight at 9:00/8:00 Central and Mountain" (also including the Mountain feed) being used to convey when the programs are set to air.

A few cable channels may not audibly refer to the Central time airtime of a program, though their promos may also visually include references to its broadcast in both the Eastern and Central time zones. So when a viewer only hears "tonight at 8:00", regardless of whether the promo visually includes it or not, it is probable that the show they are referring to is scheduled to be telecast at 7:00 p.m. in the Central Time Zone.

Some networks also broadcast an East Coast feed which includes the Eastern, Central and Mountain Time Zones, and a West Coast feed which includes Pacific Time, the Alaska Time Zone and the Hawaii–Aleutian Time Zone.

Broadcast television

Effectively, the East, Mountain and West network feeds allow prime time on broadcast television networks to end at 10:00 p.m. Central and Mountain and 11:00 p.m. Eastern and Pacific. When it first expanded its programming into prime time in April 1987, Fox became the first major broadcast network in the U.S. to offer a "common prime" schedule; this type of scheduling subtracts an hour from the prime time schedule, reducing it to two hours on Monday through Saturdays and three hours on Sundays – ending evening network programming earlier than NBC, CBS and ABC did – and continue to do (Fox did expand its Sunday primetime schedule into the 10:00 p.m. timeslot in September 1987, before giving back that hour to its stations in September 1993). The WB and UPN followed the "common prime" scheduling model when they both launched in January 1995. All of that were replaced by The CW and the MyNetworkTV program service upon their launches in September 2006.

Only the Eastern and Pacific Time Zones run prime time network programming beginning at 8:00 p.m. (7:00 on Sundays); the other four time zones in the country – Central, Mountain, Alaska and Hawaii-Aleutian – run primetime programming at 7:00 p.m. (6:00 on Sundays) – however, the major broadcast networks only simultaneously broadcast network programs to the Eastern and Central Time Zones, while the others receive all network programs separately in each zone at time slots mirroring the two easternmost U.S. time zones. Network programming in Alaska generally follows a schedule similar to that of Central Time Zone, with the stations in Anchorage broadcasting directly from the Pacific Time Zone feed without a tape delay. Thus, programs that are broadcast at 8:00 p.m. in Los Angeles and Seattle will be shown at 7:00 p.m. in Anchorage and Juneau. With the exception of local ABC affiliate KATN, network programming in Fairbanks is tape-delayed by one hour. The stations in Hawaii (all located on Oahu and based in Honolulu, with repeaters and satellite stations that relay the major network affiliates' programming to Wailuku and Hilo) also follow a schedule similar to the Central Time Zone (though the state's Fox affiliate, KHON-TV, and its satellites broadcast the network's Sunday programming on a one-hour tape delay from 7:00 to 10:00 p.m. instead of 6:00 to 9:00 p.m.).

In the territory of Guam, which is on the other side of the International Date Line from the rest of the United States, television stations broadcast prime time shows, network newscasts, and morning shows the day after they are broadcast in the mainland. However, most sports events are broadcast live. Those that are broadcast during the daytime in the mainland are shown overnight in Guam, while NBC Sunday Night Football, the World Series and other prime time telecasts are shown the next morning, typically at 9:00 or 10:00 a.m. Until its disaffiliation from NBC in 2012, the only network affiliate in American Samoa, KKHJ-LP, broadcast that network's Pacific time zone feed on a three-hour delay (details for Puerto Rico and the Virgin Islands are in the next section below).

In 2009, PBS began using Internet servers instead of separate feeds for time delaying of its programming to the network's member stations, the servers imitate a delayed program feed, broadcasting the program at the correct airtime as if it were being broadcast via satellite. This was done as PBS had upgraded its main program feed to high definition (or to widescreen digital at the very least) in December 2008, but satellite capacity allowed for only Eastern and Pacific time zone feeds, prompting the removal of the Central and Mountain time zone feeds and a shared feed for Alaska and Pacific time zones in February 2009, which created complaints from PBS stations.

For some shows, the networks must utilize a fourth feed for the Central Time Zone. Morning shows like Good Morning America, Today and CBS This Morning may start too early for viewers in the Midwest and the central South; hence, they are tape-delayed to air at 7:00 a.m. Central Time. Very rarely are these shows shown live at 6:00 a.m. Central, usually to carry breaking news or a live event occurring in the afternoon in Europe, as has been done for royal British weddings and papal ceremonies.

Not all of the network programming is strictly scheduled, however. Network soap operas, game shows and national news programs have recommended times to be broadcast, but the final scheduling for those shows – or any preemption thereof – is most often at the discretion of the local stations.

Cable and satellite television

Subscribers to cable or satellite television services may still only receive East Coast feeds for certain channels even if they reside on the West Coast. Some cable channels only offer one broadcast feed, where viewers see the same program in all time zones. For example, until it dropped the program in 2014, superstation-turned-basic cable channel WGN America telecast the noon (Central Time) newscast from WGN-TV in Chicago at 1:00 p.m. Eastern in Washington, D.C. and 10:00 a.m. Pacific in Los Angeles.

Broadcasters offer East and West Coast feeds of some basic cable channels for viewing in all time zones, allowing viewers who missed a particular program to watch it three hours earlier or later. Nickelodeon is the only American basic cable channel that transmits dual broadcast feeds to digital cable viewers (and not merely satellite viewers). An alternate feed known as Nick 2 is essentially the opposite coast's feed of Nickelodeon (the Pacific time zone feed for East Coast viewers and vice versa). The channel's main feed for the respective time zone is carried on the local cable provider's expanded basic package.

The usage of dual feeds of the same channel is a commonplace method for premium channels such as HBO, Showtime and Starz, in which the Pacific time zone feed of the primary channel is packaged with the East Coast feed of the main channel and the pay service's multiplex channels (if the premium channel has any). Most commonly, the Eastern and Pacific Time Zone feeds of only the main channel are packaged together, although some providers may also provide both coastal feeds of a premium service's multiplex channels. In some cases, cable networks (such as cable news and sports channels) "fake" the dual feed approach by recycling their same-day prime time programming during the overnight hours on a three (or four) hour cycle; in this case, the programs are automatically rebroadcast at the advertised time (or one hour later) in the Pacific Time Zone.

In Canada, distant over-the-air broadcast stations are offered by direct-broadcast satellite providers, allowing viewers to choose between the east and west feeds of a given network. The same is not true of the United States, where local network affiliates have successfully sued DBS providers to deny access to distant stations of the same network in their markets; however, the country's two major satellite providers – DirecTV and Dish Network – as well as C-band services that do not offer locally-based affiliates for most individual markets, do carry affiliates of all six broadcast networks to provide programming from at least one of them for subscribers living in smaller media markets or rural areas where a network does not have a local affiliate available on the provider, if even presently serving the given location at all. These designated stations are usually owned-and-operated stations and/or affiliates of ABC, NBC, CBS, Fox and The CW located in the Eastern and Pacific Time Zones (usually those based in New York City and Los Angeles such as Los Angeles ABC station KABC-TV and CBS' New York City station WCBS-TV). Dish Network and C-band providers also provide CW and MyNetworkTV affiliates designated as superstations (such as WPIX in New York and KTLA in Los Angeles), with Dish mainly making them available in markets where it does not carry a low-power, digital subchannel-only or non-broadcast affiliate of either network (especially in markets served by The CW's quasi-national feed for areas ranked below #98 in Nielsen Media Research market rankings, The CW Plus).

Live events

Many national live events are broadcast simultaneously nationwide – including most sporting events, national coverage of breaking news stories, the State of the Union address, presidential and Congressional election coverage, and certain award shows (such as the Academy Awards). Live events that are simulcast across the country also present special problems for local stations; for such events the networks may either advertise Eastern time only, or list the times in both Eastern and Pacific (e.g. "8 p.m. Eastern/5 p.m. Pacific"). As such, a live Sunday sporting event that is played from 4:00 to 7:00 p.m. Eastern Time preempts local 6:00 p.m. newscasts on the East Coast. Likewise, a State of the Union address that is televised at 9:00 p.m. Eastern Time preempts local 6:00 p.m. newscasts on the West Coast.

However, many award shows, most Olympic competitions, and other similar events that are broadcast live in the Eastern and Central time zones, including some that originate from Los Angeles (such as the Grammy Awards, certain reality competition shows such as Dancing with the Stars, and the live rounds of shows such as The Voice and American Idol), may be tape-delayed in the Mountain and Pacific time zones, thus making it impossible for viewers in those time zones to vote after performance episodes of live reality competition shows finish airing on the East Coast. The mechanics of the 2014 ABC series Rising Star—which allowed for live, real-time voting by viewers—would allow the insertion of live reaction segments in the event that a contestant eliminated by low vote totals in the original Eastern/Central time zone broadcast would be saved by results watching the Pacific/Mountain broadcast. However, ABC noted that the chances of West Coast votes differing substantially from other viewers was statistically small.

The practice of tape delay is due to the potentially higher West Coast viewership during prime time hours, and it also allows potentially objectionable content occurring without warning that is not allowed on broadcast television per regulations imposed by the Federal Communications Commission (such as fleeting profanities or wardrobe malfunctions) to be edited out for broadcast in the Mountain and Pacific time zones if they are shown live on the East Coast feed. When programs such as these air on tape-delay to other time zones, it is not uncommon for networks to display a graphic at the beginning of the broadcast stating that the program being shown is "recorded from an earlier live broadcast" or simply "recorded earlier". As well, when one of these program's graphics may include the display of the word "live" on screen, networks may add the abbreviations "EST" or "EDT" (for Eastern Standard Time and Eastern Daylight Time, respectively, depending on whether or not the country is on Standard or Daylight Saving Time at the time of the broadcast) as a way of advising viewers in other time zones that the "live" broadcast they are watching is actually pre-recorded and was only aired live in the Eastern Time zone (this is a common practice with tape-delayed broadcasts of American networks' morning programs).

Similarly, media coverage of New Year's Eve celebrations in New York City often leave the Central Time Zone out. Late Night with Conan O'Brien, though produced in New York City, when broadcast on New Year's Eve took advantage of its later time slot (11:37 p.m. Central time) to lampoon this inconsistency by presenting a New Year's celebration for the Central Time Zone. In some locations, New Year's Eve celebrations held in New York might be repeated or delayed one hour to correspond to the Central Time Zone. News channels such as CNN and sports channels such as ESPN that frequently broadcast live events offer a single feed that airs in all time zones. About 80 percent of American television viewers reside in the Central and Eastern time zones.

Occasionally, networks will produce and broadcast the same live event twice in one night: broadcasting once on an East Coast feed and again on a West Coast feed three hours later. This permits more viewers to watch the broadcast live in prime time (although not all), as the show can air in its usual timeslot in all markets, but incurs the expense and difficulty of delivering two live broadcasts. In some cases, the two broadcasts may intentionally differ, prompting fans to compare notes and post scenes from each version online. While rare, the technique of multiple live broadcasts has generally been used in recent times for some special live episodes of scripted programs, such as the 30 Rock episodes "Live Show" and "Live from Studio 6H", Will & Grace's "Alive and Schticking", The West Wing's "The Debate", and ER's "Ambush".

Breaking news coverage

News programs that normally air tape delayed on the West Coast, especially morning programs, may pre-empt the previously recorded program with a live broadcast for the West Coast when breaking news warrants an update to the newscast. This additional live broadcast generally replaces the first news segments of the program, while the remaining portion of the previously recorded program is used for the rest of the broadcast. When a national breaking news event occurs during the day, networks will break into regularly scheduled programming and televise a live "special report" in all time zones. Depending on the story being followed, such reports generally last no more than a few minutes before the networks resume regularly scheduled programming. On rare occasions when a major breaking news event has occurred or a political press conference (such as press briefings conducted by the President of the United States) is to be held imminently, networks will pre-empt regularly scheduled programming to run a live extended "special report" in all time zones. Coverage of breaking news events or Presidential press conferences may cause pre-emptions or delays of other network programs depending on the location and the network's scheduling practices; ABC and CBS normally delay scheduled prime time programs that are held back due to news coverage in the Eastern and Central Time Zones – and occasionally in some westward time zones depending on the length of the coverage (much in the same manner that Fox and CBS delay shows for sporting events with afternoon start times that run into prime time); NBC and Fox, however, often join their prime time schedule in progress – subjecting some programs to being pre-empted outright – unless a live program is scheduled to air.

Extended national breaking news coverage may also cause issues with the broadcasts of daytime programs, especially soap operas, which by their format are scheduled on a five-day-a-week stripped basis and are structured to carry certain storylines over into consecutive episodes. If coverage does not necessitate pre-emption of its daytime lineup in all four contiguous U.S. time zones, CBS may allow its stations in the Eastern and Central – and sometimes, Mountain – time zones to tape-delay that day's episode(s) of its soaps (The Young and the Restless and The Bold and the Beautiful) through the network's Pacific Time Zone feed for rescheduling in overnight timeslots, effectively preventing disruption to the program's airdates if an episode airs as scheduled in time zones located farther west; in contrast, ABC and NBC will generally delay that day's episode of their respective soaps (General Hospital and Days of Our Lives) to the next calendar weekday should national news coverage pre-empt them in their entirety in the Eastern and Central Time Zones, in order to allow the episode to air first-run throughout the country (this is particularly true with Days, which NBC transmits in the Eastern Time Zone first at 1:00 p.m., and is scheduled by its stations in varying timeslots depending on the market from between 12:00 and 2:00 p.m.).

Effects on local programming

Local stations and affiliates must schedule their local and syndicated programming around their respective network's feed. Because primetime programs on the East Coast feed are simulcast in two time zones, stations in the Central Time Zone are affected differently from those in the Eastern Time Zone. An hour of syndicated programming time (between 7:00 and 8:00 p.m. in the Eastern and Pacific time zones) is lost in the Central and Mountain time zones since network primetime in those areas starts at 7:00 p.m., forcing stations in Mountain or Central time (or in parts of both zones) to choose between airing their 6:00 p.m. newscast and another syndicated or locally produced program or airing shows in "blocks" preferred by syndicators (for example, Wheel of Fortune and Jeopardy! together or Entertainment Tonight and The Insider together).

The most common set of programming chosen by stations aligned with the Big Three television networks (ABC, CBS and NBC) is to air a local newscast at 5:00 p.m., national news at 5:30 p.m., another local newscast at 6:00 p.m. and syndicated programming at 6:30 p.m., though some Fox stations that maintain a newscast schedule comparable to stations tied to the Big Three (commonly stations that were former ABC, NBC and CBS affiliates themselves) carry a 60- or 90-minute block of news from 5:00 to 6:00 (or 6:30) p.m. with an additional half-hour of local news in the 5:30 p.m. timeslot as Fox does not air a national evening newscast; a few stations not affiliated with the Big Four networks, such as WGN-TV, KTLA in Los Angeles and WJXT in Jacksonville, Florida, follow a similar scheduling format with their early evening newscasts. Most Big Three affiliates in the Eastern and Pacific time zones follow this early evening newscast model as well, running a 90-minute block of news from 5:00 to 6:30 p.m., particularly if they run a network's national evening newscast at 6:30 p.m. Eastern and Pacific Time. Some stations, regardless of time zone, even show a newscast from 6:00 to 7:00 p.m., which if run on a network station in the Central or Mountain time zones would lead into primetime network programming. Some television stations (such as WKYC and WJW in Cleveland, Ohio, or WJAR in Providence, Rhode Island) have recently begun using the fact that primetime in the Eastern Time Zone begins at 8:00 p.m. to their advantage by carrying a newscast during the 7:00 p.m. hour, generally in order to attract viewers who work longer days and cannot return home to watch a 5:00 or 6:00 p.m. newscast.

Many stations that do not carry a newscast in the 6:00 p.m. timeslot in the Central Time Zone (commonly independent stations and most affiliates of non-historical networks like Fox – which has some stations that air a 6:00 p.m. newscast, though this is not entirely commonplace – The CW and MyNetworkTV) air situation comedies or other types of syndicated programming, such as reality series or game shows, during that hour. Many stations in the Central Time Zone tend to air one or both parts of the syndicated block at 5:00 p.m. or even earlier. Another more recent dilemma of the 7:00 p.m. primetime start is that a combination of longer commutes and work hours than in the past have caused many people to not come home from work until after 7:00 p.m., cutting into the potential ratings of shows that start at this time. Of course, the reverse is also true since simultaneous broadcasts offer viewers the chance to watch "prime time television" without having to stay awake until 11:00 p.m.

Local programming such as locally produced newscasts are not typically affected as many stations air their morning newscast at 4:00, 4:30, 5:00 or 5:30 a.m., and their early evening newscasts at 5:00 and/or 6:00 p.m.; however, the late evening newscast is affected due to the differences in time between time zones, meaning that if the late local news starts at 10:00 p.m. Central time on one network station, an affiliate of the same network in the Eastern Time Zone airs its newscast at 11:00 p.m.; network evening newscasts on CBS, ABC, and NBC are affected since they are usually scheduled to air at 6:30 p.m. Eastern Time (barring preemption due to network sports coverage or at the discretion of the local station, breaking news or severe weather coverage) in order to sync up with its simultaneous broadcast in the Central Time Zone. Midday newscasts are not necessarily affected, depending on whether the station's affiliated network schedules their daytime lineup simultaneously in the Eastern and Central Time Zones (as with ABC and CBS) or just to the Eastern Time Zone first (as with NBC). The late night program lineups on ABC, CBS, NBC and Fox are also similarly timeshifted, airing a half-hour later (after a newscast or syndicated programming if the station does not run news programming) but are shifted due to the time zone differences (a bigger issue with first-run late night programs that air after 12:30 a.m. Eastern Time since the later start time may subject these programs to a potentially decreased audience). Many Fox, CW and MyNetworkTV affiliates, and some independent stations carry a prime time newscast that is similarly affected by the timeshifting of the prime time schedule, meaning that if said late evening newscast starts at 9:00 p.m. Mountain Time on one network station, an affiliate of the same network in the Pacific time zone would air its news at 10:00 p.m.

Changes for Daylight Saving Time

Time changes for daylight saving time may result in broadcast television stations and cable channels accommodating the time changes by altering their schedules to allow programs to continue to air at the same time year-round. Due to the structure of daylight saving time (which begins and ends at 2:00 a.m. in each time zone on the respective dates), the switch from standard time to daylight saving time on the second Sunday in March requires clocks to be advanced by one hour to 3:00 a.m., and the reversion to standard time on the first Sunday in November requires clocks to be moved back by one hour to 1:00 a.m.

During the switch from standard time to daylight saving time, television stations and cable networks will usually offset the loss of one hour by eliminating programming otherwise scheduled during the 2:00 a.m. hour on Saturday night/early Sunday morning. Conversely, as one hour is gained when reverting to standard time, networks may offset the time change by adding an hour of additional entertainment programming not normally scheduled on Saturday night/early Sunday morning during the rest of the year to allow certain programs to air at their regularly scheduled airtime (for example, Disney Channel will add an hour of its original series at 1:00 a.m. Eastern Daylight Time in order to allow its Saturday late night film block to air its regular 2:30 a.m. slot, after the reversion to standard time). Cable channels airing paid programming during the late night period may choose not to add entertainment shows and instead add an additional hour of infomercials (as an example, Discovery Channel usually extends its infomercial block, which normally begins at 3:00 a.m. Eastern Time, by one hour; similarly, E! adds one hour of infomercials in the 2:00 a.m. EDT slot, normally ceded to general entertainment programming, followed by one hour of entertainment programs, then a block of infomercials starting in their normal 4:00 a.m. Eastern Standard Time slot).

Some areas of the U.S. do not observe daylight saving time, leading to the following changes; though in all cases, sports and other event telecasts that are broadcast live always begin an hour earlier, depending on time zone:

• Stations in Arizona (only Navajo Nation reservations observe daylight saving time) change from the live Mountain Time feed to a delay from the Eastern/Central feed when daylight saving time begins, to preserve a 7:00 p.m. start time. This is also the case for live syndicated radio programs, such as The Rush Limbaugh Show, which air live during the winter and are delayed one hour during daylight saving time;
• Programs airing on stations in Puerto Rico and the United States Virgin Islands, which are in the Atlantic Time Zone and do not observe daylight saving time, start at the same clock time as in the Eastern Time Zone when the latter is on daylight saving time. Otherwise, primetime is scheduled at one clock hour later. This is because affiliates there receive their programs from the Eastern/Central Time master control (a similar arrangement occurs in Bermuda, which is a British territory but is the home of three affiliates of U.S. networks).
• In Alaska, Hawaii, Guam and American Samoa, primetime shows are delayed by an additional hour.

Scheduling variations for areas located between two time zones

A handful of U.S. media markets lie on bordering time zones (Pacific/Mountain, Mountain/Central or Central/Eastern). While stations will carry a program in all counties that are part of the Designated Market Area, counties on either side of the market will air network programming simultaneously one hour earlier or later, depending on location:

• A number of media markets based in Eastern Time Zone cities have outlying areas in the Central Time Zone, including Atlanta and Columbus, Georgia; Louisville, Kentucky; Chattanooga and Knoxville, Tennessee; Escanaba, Michigan; and Terre Haute, Indiana. However, since the usual primetime lineup is fed to them at the normal times for their zones, the effects are minimal in contrast to the following examples (although the morning programs are seen in those areas an hour ahead of their normal time for each time zone; as a result, Today, Good Morning America and CBS This Morning start at 6:00 a.m. in those areas as opposed to 7:00 a.m.), and merely consist of mentioning both times in station promotions for viewer reference.
• Fox affiliate KECY-TV (and its ABC-affiliated subchannel), which is licensed to El Centro, California, starts primetime programming at either 6:00 or 7:00 p.m. local time, depending on Daylight Saving Time status, because Yuma County in Arizona shares a media market with El Centro. All other stations in California start primetime network shows at 8:00 p.m.
• Satellite stations in western North Dakota, within the Mountain time zone, have 6:00 p.m. starts to primetime rather than the usual 7:00 p.m. because the primary stations are in either Bismarck or Minot in the Central Time Zone. These stations also serve areas in eastern Montana, which also observes the Mountain Time Zone.
• The four counties in western Kansas that are located within the Mountain Time Zone receive prime-time programming from 6:00 to 9:00 p.m. since they are part of the Wichita-Hutchinson DMA (the remainder of which lies within the Central Time Zone), and the stations operate as satellites of the main feed in Wichita.
• Viewers in Lincoln County, Montana, which observes Mountain Time, receive primetime shows from the Pacific Time Zone-based Spokane, Washington DMA across the Idaho Panhandle two hours later than locations elsewhere in the Mountain Time Zone – from either 9:00 to 11:00 p.m. (or midnight) Mountain Time Monday through Saturday and 8:00 to 11:00 p.m. (or midnight) on Sunday, depending on the network.

Other scheduling variations

• In Sacramento, California, CBS owned-and-operated station KOVR broadcasts the network's schedule an hour behind other stations in the Pacific Time Zone using the Central/Mountain scheduling from 7:00 to 10:00 p.m., nominally to provide an advantage for its local newscast airing at 10:00 p.m. against weaker competition from the area's Fox affiliate KTXL than the 11:00 p.m. newscasts on the NBC and ABC stations; it is presently the only major network affiliate to schedule primetime programs in this manner. During the 1990s, CBS station KPIX and then-NBC affiliate KRON-TV in San Francisco aired their network primetime lineups an hour early in order to compete against Fox affiliate (now owned-and-operated station) KTVU's market-leading 10:00 p.m. newscast, though both stations moved their late evening newscasts and network primetime lineups back to their traditional timeslots as they were unsuccessful in competing with KTVU.
• In Glendive, Montana, CBS/NBC affiliate KXGN-TV holds a local monopoly and has long used CBS' Eastern Time Zone feed to run its prime time network programming from 6:00 to 9:00 p.m. Mountain Time. This originally allowed it to run NBC programming after 9:00 p.m. on the same channel; when the NBC affiliation was moved to a digital subchannel of the station, KXGN began filling the post-9:00 p.m. slot with syndicated programming.

See also

• East Coast bias
• Timeshifting
• Space shifting (also known as place shifting)