Send payment and clock back (5)
I believe the answer is:
remit
'send payment' is the definition.
(I've seen this before)
'clock back' is the wordplay.
'clock' becomes 'timer' (something which times).
'back' says the letters should be written backwards.
'timer' back-to-front is 'REMIT'.
'and' acts as a link.
(Other definitions for remit that I've seen before include "Send back; scope of authority" , "Send - scope of one's duties" , "Send; brief" , "Desist from" , "Send (money) by post" .)