Match about to be held in time (5)
I believe the answer is:
agree
'match' is the definition.
(agreeing is a kind of matching)
'about to be held in time' is the wordplay.
'about' becomes 're' (regarding**).
'to be held in' means one lot of letters goes inside another.
'time' becomes 'age' (age is a kind of time).
're' put into 'age' is 'AGREE'.
(Other definitions for agree that I've seen before include "Settle" , "grant" , "confess?" , "Be of one mind" , "Consent required" .)