A long time taken up in scene of conflict (5)
I believe the answer is:
arena
'scene of conflict' is the definition.
(I've seen this in another clue)
'a long time taken up' is the wordplay.
'a' becomes 'an'.
'long time' becomes 'era' (a long period of time).
'taken up' is a reversal indicator.
'an'+'era'='anera'
'anera' reversed gives 'ARENA'.
'in' is the link.
(Other definitions for arena that I've seen before include "Circus ring" , "An era (anag.)" , "Scene of action" , "Amphitheatre's central space" , "place involving conflict?" .)