Charity event possibly demanding payment: about time! (4)
I believe the answer is:
fete
'charity event possibly' is the definition.
(a fete might be a charity event)
'payment about time' is the wordplay.
'payment' becomes 'fee' (payment for a job).
'about' is an insertion indicator.
'time' becomes 't' (abbreviation).
'fee' enclosing 't' is 'FETE'.
'demanding' is the link.
(Other definitions for fete that I've seen before include "Celebrate; village fair" , "Fundraising event" , "Wine and dine" , "Organised series of acts and performances" , "Village event" .)