Don clothes on time for event (8)
I believe the answer is:
dressage
'for event' is the definition.
(I've seen this before)
'don clothes on time' is the wordplay.
'don clothes' becomes 'dress' (I've seen this before).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'time' becomes 'age' (an age is a period of time).
'dress'+'age'='DRESSAGE'
(Other definitions for dressage that I've seen before include "equestrian activity" , "Training for competition" , "Event for rider" , "Equestrian performance" , "Manoeuvres of a horse in response to body signals by its rider" .)