He is on time for a robbery (5)
I believe the answer is:
heist
'robbery' is the definition.
(heist is a kind of robbery)
'he is on time' is the wordplay.
'on' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'he'+'is'+'t'='HEIST'
'for a' acts as a link.
(Other definitions for heist that I've seen before include "Audacious robbery" , "Robbery, often at gunpoint" , "crime?" , "Armed hold-up (sl.)" , "criminal activity" .)