I'm open about one for those who hate waiting (9)
I believe the answer is:
impatient
'those who hate waiting' is the definition.
(I've seen this before)
'i'm open about one' is the wordplay.
'open' becomes 'patent' (I've seen this in another clue).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'patent' enclosing 'i' is 'patient'.
'im'+'patient'='IMPATIENT'
'for' is the link.
(Other definitions for impatient that I've seen before include "Restless; intolerant" , "Fidgety" , "Restless or short of temper" , "Over-eager" , "fed up with waiting time?" .)