In American television, early prime time is a programming practice of airing television prime time programming an hour earlier than normal. It is most applicable in the Pacific Time Zone, where prime time programming generally airs from 8 to 11 p.m. (as on the East Coast), as opposed to 7 to 10 p.m. as in the Central and Mountain time zones.
Interest by network affiliates on the West Coast in moving their prime time schedules up an hour to account for changing lifestyles and viewing habits took root most notably in Northern California, where NBC permitted KCRA-TV in Sacramento to experiment with an early prime time schedule beginning in 1991. In nearby San Francisco, KRON-TV (the NBC affiliate) and KPIX-TV (the CBS affiliate) both began using early prime time in 1992; KPIX was joined by KMST in Monterey in adopting early prime. In the case of the San Francisco stations, the NBC and CBS affiliates wanted to compete with the dominant 10 p.m. newscast of Fox affiliate KTVU. However, ABC refused to switch its San Francisco station, KGO-TV, and generally barred its affiliates from adopting the practice. While the only stations to adopt early prime were in Northern California, other stations in the Pacific Time Zone were supportive of the idea.
Early prime improved the stations' ratings for their late newscasts, moved from 11 to 10 pm, but reduced ratings for the first hour of prime time. It also cost the stations valuable local advertising inventory in the 7 to 8 p.m. hour, known as prime access, when stations air syndicated shows. KMST reverted to normal prime time after a year in January 1993, largely for technical and financial reasons. Under strong pressure by NBC, KCRA and KRON abandoned early prime in September 1993, while KPIX continued the practice until 1998; it was credited for raising ratings for The Late Show with David Letterman. The last new network affiliate to adopt early prime scheduling was KOVR in Sacramento, which switched from ABC to CBS in 1995 and concurrently began airing prime time at 7 pm. KOVR continues this practice, even after its acquisition by CBS in 2005.