Good time for an explosion (4)
I believe the answer is:
boom
I believe 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' is the 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" .)