When finished, take a quick look (4,4)
I believe the answer is:
once over
'a quick look' is the definition.
(as in giving something the once-over)
'when finished' is the wordplay.
'when' becomes 'once' (synonyms).
'finished' becomes 'over' (over can mean finished or ended).
'once'+'over'='ONCE-OVER'
'take' acts as a link.
(Other definitions for once over that I've seen before include "quick read?" , "inspection" , "Quick survey" , "examination" .)