Fool is on time to lend a hand (6)
I believe the answer is:
assist
'lend a hand' is the definition.
(I've seen this before)
'fool is on time' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'on' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'ass'+'is'+'t'='ASSIST'
'to' is the link.
(Other definitions for assist that I've seen before include "Work with N help" , "Pass to scorer" , "Give help" , "Understand by instinct" , "Help to make" .)