Turn back the clock and relax (5)
I believe the answer is:
remit
'relax' is the definition.
(I've seen this before)
'turn back the clock' is the wordplay.
'turn back' says the letters should be written backwards.
'the clock' becomes 'timer' (something which times).
'timer' back-to-front is 'REMIT'.
'and' acts as a link.
(Other definitions for remit that I've seen before include "Send; abate; cancel" , "Orders" , "committee's brief" , "Put off" , "Desist from" .)