Time a chap is overcome by marijuana (7)
I believe the answer is:
weekend
'time' is the definition.
(I've seen this before)
'a chap is overcome by marijuana' is the wordplay.
'a chap' becomes 'Ken' (man's name).
'is overcome by' is an insertion indicator.
'marijuana' becomes 'weed' (synonyms).
'ken' going into 'weed' is 'WEEKEND'.
(Other definitions for weekend that I've seen before include "Occasional" , "Sat. and Sun." , "Saturday plus Sunday" , "time for game?" , "time off work?" .)