Times up in West perhaps? (5)
I believe the answer is:
maybe
'perhaps?' is the definition.
('maybe' can be a synonym of 'perhaps')
'times up in west' is the wordplay.
'times' becomes 'by' (both can mean 'multiplied by').
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'in' indicates putting letters inside.
'west' becomes 'Mae' (I've seen this before).
'by' in reverse letter order is 'yb'.
'yb' placed within 'mae' is 'MAYBE'.
(Other definitions for maybe that I've seen before include "Perhaps, might happen" , "Perhaps, possibly" .)