Send clock, perhaps, up (5)
I believe the answer is:
remit
'send' is the definition.
(I've seen this before)
'clock perhaps up' is the wordplay.
'clock perhaps' becomes 'timer' (something which times).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'timer' backwards is 'REMIT'.
(Other definitions for remit that I've seen before include "Defer" , "Pay for timer" , "Cancel - terms of reference" , "Job specification" , "Orders" .)