Fine female in time becomes foolish (5)
I believe the answer is:
daffy
'foolish' is the definition.
(thesaurus)
'fine female in time' is the wordplay.
'fine' becomes 'f' (abbreviation).
'female' becomes 'f' (abbreviation).
'in' is an insertion indicator.
'time' becomes 'day' (day is a kind of time**).
'f'+'f'='ff'
'ff' going into 'day' is 'DAFFY'.
'becomes' acts as a link.
(Other definitions for daffy that I've seen before include "Silly, mildly eccentric" , "foolish" , "Silly, eccentric (colloq.)" , "duck on screen" , "Cuckoo" .)