Make up at lunchtime, perhaps (5)
I believe the answer is:
atone
'make up' is the definition.
(to atone for something is to make up for it)
'at lunchtime perhaps' is the wordplay.
'lunchtime perhaps' becomes 'one' (I've seen this in another clue).
'at'+'one'='ATONE'
(Other definitions for atone that I've seen before include "Turn away from sin and do penance" , "Pay the price" , "Make amends (for something)" , "Make reparation for a misdeed" , "remedy" .)