After success briefly had opening they retire (3,3,3)
I believe the answer is:
hit the hay
'retire' is the definition.
(synonyms)
'after success briefly had opening they' is the wordplay.
'after' means one lot of letters go next to another.
'success' becomes 'hit' (hit is a kind of success).
'briefly' means to remove the last letter.
'opening' indicates putting letters inside (some letters open a gap in others).
'had' with its last letter taken off is 'ha'.
'ha' put within 'they' is 'thehay'.
'hit' next to 'thehay' is 'HIT THE HAY'.
(Other definitions for hit the hay that I've seen before include "(retired)" , "Go to bed (informal)" , "Retire to bed (informal)" , "Retire for the night (informal)" , "Crash" .)