Quick look is barely sufficient when lacking time (4)
I believe the answer is:
scan
'quick look' is the definition.
(I've seen this before)
'barely sufficient when lacking time' is the wordplay.
'barely sufficient' becomes 'scant' (I've seen this before).
'when lacking' suggests deleting specific letters.
'time' becomes 't'.
'scant' with 't' taken out is 'SCAN'.
'is' acts as a link.
(Other definitions for scan that I've seen before include "Survey - check-up" , "Perusal" , "Examine intensely -- examine superficially" , "Read superficially" , "Type of examination" .)