Good time for an explosion (4)
I believe the answer is:
boom
This clue is a double definition.
'good time' is the first definition.
(I've seen this in another clue)
'an explosion' is the second definition.
(thesaurus)
'for' acts as a link.
(Other definitions for boom that I've seen before include "Pole for overhead microphone - deep sound" , "Loud noise - business increase" , "Deep hollow sound" , "Period of prosperity - explosive sound - sailing boat's spar" , "When business is great, opposite to bust" .)