Completed fitting -- not before time! (7)
I believe the answer is:
overdue
'not before time' is the definition.
(after time)
'completed fitting' is the wordplay.
'completed' becomes 'over' ('over' can be a synonym of 'completed').
'fitting' becomes 'due'.
'over'+'due'='OVERDUE'
(Other definitions for overdue that I've seen before include "Late like unpaid bill" , "Late for payment" , "Late arriving" , "Not consumed" , "(Of library books) late" .)