Scheduled collection beginning (5)
I believe the answer is:
onset
'beginning' is the definition.
(I know that beginning can be written as onset)
'scheduled collection' is the wordplay.
'scheduled' becomes 'on' (I've seen this in other clues).
'collection' becomes 'set' (set is a kind of collection).
'on'+'set'='ONSET'
(Other definitions for onset that I've seen before include "Kick-off" , "Start - attack" , "Appearance of" , "Cast stone in attack" , "Beginning; violent attack" .)