Time opponent's taken over me is not significant (7)
I believe the answer is:
trivial
'is not significant' is the definition.
(I've seen this before)
'time opponent's taken over me' is the wordplay.
'time' becomes 't' (abbreviation).
'opponent' becomes 'rival' (a rival is an opponent or enemy).
'taken over' indicates putting letters inside (some letters taken over or around others).
'me' becomes 'I'.
'rival' enclosing 'i' is 'rivial'.
't'+'rivial'='TRIVIAL'
(Other definitions for trivial that I've seen before include "Footling" , "Very easy" , "Petty, piffling" , "Of little substance or significance" , "Of little importance" .)