Finished before time — that's clear (5)
I believe the answer is:
overt
'clear' is the definition.
(thesaurus)
'finished before time' is the wordplay.
'finished' becomes 'over' ('over' can be similar in meaning to 'finished').
'before' is a charade indicator (letters next to each other).
'time' becomes 't'.
'over'+'t'='OVERT'
'that's' acts as a link.
(Other definitions for overt that I've seen before include "Open and undisguised" , "Patent, evident" , "Not locked away" , "Open and unconcealed" , "This is not hard to see" .)