The Central Time Zone observes standard time by subtracting six hours from UTC during standard time (UTC−6) and five hours during daylight saving time (UTC−5). The clock time in this zone is based on the mean solar time of the 90th degree meridian west of the Greenwich Observatory.
In the United States and Canada, this time zone is generically called Central Time (CT). Specifically, it is Central Standard Time (CST) when observing standard time (Winter), and Central Daylight Time (CDT) when observing daylight saving (Summer). In Mexico this time is known as the Central Zone.
The Canadian provinces and territories that observe Central Time in part with another time zone (other time zone):
Part in Eastern Time
The states of Mexico that observe Central Time in their entirety:
The states of the Mexico that observe Central Time only in part with another time zone (other time zone).
In Oceania, the Chilean Easter Island also belongs to this time zone.
In some areas, starting in 2007, the local time changes from CST to CDT at 02:00 LST to 03:00 LDT on the second Sunday in March and returns at 02:00 LDT to 01:00 LST on the first Sunday in November. Mexico decided not to go along with this U.S.-led change and observes DST from the first Sunday in April to the last Sunday in October.
Also, an hour of syndicated programming time (between 7:00 p.m. and 8:00 p.m. in the Eastern Time Zone) is lost since network prime time starts at 7:00 p.m. Central, forcing TV stations to choose between airing their 6:00 p.m. newscast and a program, or airing shows in 'blocks' preferred by syndicators (for example, Wheel of Fortune and Jeopardy! together, or Entertainment Tonight and The Insider). 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. The most common set of programming chosen by the big three television networks (ABC, CBS, and NBC) is to air a newscast at 5:00 p.m., national news at 5:30 p.m., local news at 6:00 p.m., and syndicated programming at 6:30 p.m. Some stations even show a newscast from 6:00 to 7:00 p.m. Another more recent dilemma of the 7:00 p.m. prime time 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, as simultaneous broadcasts offer viewers the chance to watch "prime time television" without having to stay awake until 11:00 p.m.
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, when broadcast on New Year's Eve (as it does not air on weekends) takes advantage of its later time slot (11:35 p.m. Central) to lampoon this inconsistency and produce its own New Year's countdown for television viewers in the Central Time Zone, although most Central Time local network affiliates usually broadcast Conan after covering their own regional New Year's Eve celebrations. In some locations, New York's New Year's Eve celebration might be repeated or delayed one hour to correspond to the Central Time zone.
Interestingly, U.S. broadcast networks do tape delay in the other two continental U.S. time zones for prime-time programmes except during sporting events and other selected live events such as election night and Academy Awards. The Mountain Time Zone is tape-delayed one hour and the Pacific Time Zone three hours from original broadcasts, so that shows match the broadcast times of the Central and Eastern Time Zones respectively (i.e. prime time begins at 7:00 p.m. MT and 8:00 p.m. PT following the same order of programming as the other two time zones). In order to keep up with these differences in time zones, most general-entertainment cable networks offer 2 feeds, one for viewers in the Eastern and Central time zones and another for the Mountain and Pacific time zones.
Canadian broadcasting networks, with 5½ time zones to span and a larger percentage of its audience residing in the Mountain Time Zone than in the Central Time Zone (which only has one significant metropolitan area (Winnipeg, Manitoba), sometimes are able to avoid these issues by airing prerecorded programs on local time (except Newfoundland time), although adjustments are often still made, particularly on private networks (mainly due to the influence of U.S. television). This is particularly a problem in Saskatchewan as Central Standard Time is used year round, choosing not to change to daylight saving time during the summer. While Saskatchewan, Manitoba and parts of northwestern Ontario share the same clock setting during the winter season, Saskatchewan and Alberta share the same clock setting during the summer season, despite the fact that Alberta is in the Mountain Time Zone. Schedules must be adjusted for the summer season.
The problem is largely moot in Mexico and other parts of Latin America because of the lack of significant other time zones.