Age occasionally overlooked at film set (4)
I believe the answer is:
time
'age' is the definition.
(an age is a period of time)
'occasionally overlooked at film set' is the wordplay.
'occasionally overlooked' indicates alternate letters (letters removed at regular intervals).
'at'+'film'+'set'='atfilmset'
The alternate letters of 'atfilmset' are 'TIME'.
(Other definitions for time that I've seen before include "It's done in prison" , "Prison sentence; tempo" , "Procrastination is the thief of ." , "The father of Truth, presumably" , "Rhythm" .)