Bleach it inside at what time? (6)
I believe the answer is:
whiten
'bleach' is the definition.
(I know that bleach is a more specific form of the action the whiten)
'it inside at what time?' is the wordplay.
'inside' is an insertion indicator.
'at what time?' becomes 'when' (I've seen this in another clue).
'it' placed into 'when' is 'WHITEN'.
(Other definitions for whiten that I've seen before include "Blanch" , "Bleach" , "Turn pale" , "free from guilt" , "New hit (anag.)" .)