The most common and most likely answer to this crossword clue is the 6 plus 2 plus 7 letter word REPENT AT LEISURE
I've seen this crossword clue in The Guardian
R
E
P
E
N
T
A
T
L
E
I
S
U
R
E
Buddy explains!
The straight part
We know that "second half of proverb" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case second half of proverb = repent at leisure.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.