Later in the day not on being drunk (5)
I believe the answer is:
tight
'being drunk' is the definition.
(I've seen this before)
'later in the day not on' is the wordplay.
'later in the day' becomes 'tonight' (I've seen this before).
'not' is a deletion indicator.
'tonight' with 'on' taken away is 'TIGHT'.
(Other definitions for tight that I've seen before include "lack of money" , "Inebriated" , "South American nation" , "Unlikely to be choosing the present" , "Drunk; restricted" .)