Once I got time for leave (4)
I believe the answer is:
exit
'for leave' is the definition.
(synonyms)
'once i got time' is the wordplay.
'once' becomes 'ex' (prefix meaning former or onetime).
'got' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'ex'+'i'+'t'='EXIT'
(Other definitions for exit that I've seen before include "Withdrawal" , "[DOOR] ?" , "Depart" , "Player's departure" , "Sudden rush of pleasure" .)