Job behind time — enquire (4)
I believe the answer is:
task
'job' is the definition.
(synonyms)
'behind time enquire' is the wordplay.
'behind' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'enquire' becomes 'ask' (to enquire is to ask or question).
't'+'ask' is 'TASK'.
(Other definitions for task that I've seen before include "exercise" , "Set piece of work" , "Piece of work to be done" , "Difficult piece of work" , "Give mission" .)