The most common and most likely answer to this crossword clue is the 5 plus 4 letter word PRIME TIME
I've seen this crossword clue in The Guardian
P
R
I
M
E
T
I
M
E
More clues leading to the result PRIME TIME
Buddy explains!
The straight part
We know that "when most are watching" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case when most are watching = prime time.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRIME TIME mean?
PRIME TIME adjective- Showing during prime time.