21 down
The
peak
hour,
dinner
time?
(6)
The peak hour, dinner time? (6)
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The definition is at the beginning of the clue.
How the clue works
The peak is your definition — the highest point. Then the wordplay builds it up: H is the standard abbreviation for hour, and eight is a classic dinner time (8 o'clock), so put them together and you've got it.