Idle moment has passed (4,4)
I believe the answer is:
tick over
'idle' is the definition.
(I know that idle can be written as tick over)
'moment has passed' is the wordplay.
'moment' becomes 'tick' (both can mean a very short amount of time).
'has' says to put letters next to each other.
'passed' becomes 'over' (I've seen this before).
'tick'+'over'='TICK OVER'
(Other definitions for tick over that I've seen before include "(Of engine) run slowly in neutral" , "Run smoothly (or very slowly?)" , "(Of engine) idle" , "Just keep going like idling engine" .)