Finished on time, that's obvious (5)
I believe the answer is:
overt
'obvious' is the definition.
(similar in meaning)
'finished on time' is the wordplay.
'finished' becomes 'over' (over can mean finished or ended).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'time' becomes 't' (abbreviation).
'over'+'t'='OVERT'
'that's' acts as a link.
(Other definitions for overt that I've seen before include "Open and obvious" , "Not locked away" , "This is not hard to see" , "Open to view" , "Clear" .)