Start work at nine, about? Good! (7)
I believe the answer is:
opening
'start' is the definition.
(opening is a kind of start)
'work at nine about? good' is the wordplay.
'work' becomes 'op' (abbreviation for opus**).
'at' says to put letters next to each other.
'about?' shows that the letters should be reversed in order (I've seen 'about' mean this).
'good' becomes 'g' (abbreviation).
'nine' written backwards gives 'enin'.
'op'+'enin'+'g'='OPENING'
(Other definitions for opening that I've seen before include "Initial" , "Rent" , "premiere" , "Orifice; opportunity" , "Kicking off" .)