Hard work and good service -- on time (5)
I believe the answer is:
'hard work' is the definition.
(graft can mean working hard)
'good service on time' is the wordplay.
'good' becomes 'g' (abbreviation).
'service' becomes 'raf' (Royal Air Force).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'time' becomes 't' (abbreviation).
'and' acts as a link.
(Other definitions for graft that I've seen before include "Hard work; bribery" , "Means of propagation - hard work?" , "Hard work - swindle" , "Transfer of tissue - hard work!" , "Labour" .)