Time to return for discharge (4)
I believe the answer is:
emit
'discharge' is the definition.
(emitting is a kind of discharging)
'time to return' is the wordplay.
'to return' says the letters should be written backwards.
'time' written backwards gives 'EMIT'.
'for' is the link.
(Other definitions for emit that I've seen before include "Conductor; telegram (US)" , "Let out" , "Send out in time" , "Give off or discharge" , "Give out (eg light)" .)