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' (chemical symbol).
'on' is a charade indicator (letters next to each other).
'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)" .)