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' means one lot of letters go next to another (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" .)