After a time, crewman is conveniently close (2,4)
I believe the answer is:
at hand
'conveniently close' is the definition.
(I've seen this before)
'after a time crewman' is the wordplay.
'after' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'crewman' becomes 'hand' (hand is a kind of crewman).
'a' next to 't' is 'at'.
'at'+'hand'='AT HAND'
'is' acts as a link.
(Other definitions for at hand that I've seen before include "Imminent" , "Close by, within reach" , "Within easy reach" , "Close or nearby - just reach" , "Like a neighbour" .)