The most common and most likely answer to this crossword clue is the 9 letter word SHOWTIMES
S
H
O
W
T
I
M
E
S
Buddy explains!

The straight part
We know that "when entertainments begin" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case when entertainments begin = showtimes.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.
Crossword Answer definitions
SHOWTIMES noun- The time at which an entertainment event is set to begin.
- The time for action.