All there is to do when eg watch wound back (5)
I believe the answer is:
remit
'all there is to do' is the definition.
(remit can mean someone's responsibilities)
'eg watch wound back' is the wordplay.
'eg watch' becomes 'timer' (a watch might be used to time something).
'wound back' shows that the letters should be reversed in order.
'timer' in reverse letter order is 'REMIT'.
'when' is the link.
(Other definitions for remit that I've seen before include "forward" , "Timer (anag.)" , "Pay for timer" , "Desist from" , "Put off" .)