Send clock back? (5)
I believe the answer is:
remit
'send' is the definition.
(I've seen this in another clue)
'clock back' is the wordplay.
'clock' becomes 'timer' (something which times).
'back' says the letters should be written in reverse.
'timer' written backwards gives 'REMIT'.
(Other definitions for remit that I've seen before include "send money, maybe" , "Pardon (a sin)" , "Area of responsibility" , "forward" , "Send payment for timer" .)