Send clock up? (5)
I believe the answer is:
remit
'send' is the definition.
(I've seen this before)
'clock up?' is the wordplay.
'clock' becomes 'timer' (something which times).
'up?' shows that the letters should be reversed in order (in down clue: letters go upwards).
'timer' backwards is 'REMIT'.
(Other definitions for remit that I've seen before include "Scope - send money" , "Maybe suspend" , "Send; abate; cancel" , "Send - terms of reference" , "Cancel - terms of reference" .)