Recital isn't arranged ahead of time for musician (12)
I believe the answer is:
clarinettist
'musician' is the definition.
(clarinettist is a kind of musician)
'recital isn't arranged ahead of time' is the wordplay.
'arranged' is an anagram indicator.
'ahead of time' becomes 't' (I've seen this in other clues).
'recital'+'isnt'='recitalisnt'
'recitalisnt' is an anagram of 'clarinettis'.
'clarinettis'+'t'='CLARINETTIST'
'for' acts as a link.
(Other definitions for clarinettist that I've seen before include "Cats in litter (anag) -- woodwind player" , "Musician, like Benny Goodman, say" .)