Suitable moment for some fun (4,4)
I believe the answer is:
good time
'some fun' is the definition.
'suitable moment' is the wordplay.
'suitable' becomes 'good' ('good' can be similar in meaning to 'suitable').
'moment' becomes 'time' (time is a kind of moment).
'good'+'time'='GOOD-TIME'
'for' acts as a link.
(Other definitions for good time that I've seen before include "Seeking pleasure" , "in which one is early" .)