Prime time refers to the block of programming on American television during the middle of the evening. In the United States, television networks broadcast their prime time programming in two blocks: One for the Eastern, Central, and Mountain time zones, and one for the Pacific, Alaskan, and Hawaiian time zones. The generally accepted times considered to be traditional prime time are 8:00pm to 11:00pm Eastern and Pacific and 7:00pm to 10:00pm Central and Mountain Monday-Saturday. Sundays extend an hour earlier to begin at 7:00pm Eastern and Pacific and 6:00pm Central and Mountain. With the addition of newer networks such as The FOX Network, The WB, and UPN, there now is considered a common prime separate from traditional prime. Common prime is 8:00pm to 10:00pm Eastern and Pacific and 7:00pm to 9:00pm Central and Mountain Monday-Saturday with the same hour extension on Sundays.
Prime time is the block of time with the most viewers and is generally where television networks and local stations reap much of their advertising revenues. The existence of prime time in the United States is largely an artifact of now repealed regulations of the Federal Communications Commission which limited the number of hours that a network can require its affiliates to broadcast.
Other blocks of programming include the daytime, early fringe, early news, early access, late news, late fringe and overnight dayparts. Typically these dayparts describe the 24 hours of broadcasting Monday-Friday.
Additionally, networks may also choose to provide local affiliates the opportunity to air sports events which may fall outside of standard designated network broadcast times.