prime time

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The evening hours, generally between 7 and 11 P.M., when the largest television audience is available.

Wiktionary

1. n. obsolete Spring.
2. n. obsolete A new period or time of youthfulness; the beginning of something.
3. n. television, radio The block of programming on television during the middle of the evening, usually between 19:00 and 23:00
4. adj. television, radio Showing during prime time.

WordNet 3.0

1. n. the hours between 7 and 11 p.m. when the largest tv audience is available