Reduce copper on time (3)
I believe the answer is:
cut
'reduce' is the definition.
(I know that reduce can be written as cut)
'copper on time' is the wordplay.
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'time' becomes 't' (abbreviation).
'cu'+'t'='CUT'
(Other definitions for cut that I've seen before include "reduced" , "Incise" , "Sever - hurt - snub" , "Wound" , "Reduce; joint (of meat)" .)