Cheese fine initially, but not long (5)
I believe the answer is:
brief
'not long' is the definition.
(brief means short)
'cheese fine initially' is the wordplay.
'cheese' becomes 'brie' (Brie is an example).
'initially' suggests taking the first letters.
The initial letter of 'fine' is 'f'.
'brie'+'f'='BRIEF'
'but' is the link.
(Other definitions for brief that I've seen before include "Remit" , "Terse" , "Concise; short-lived" , "Short or concise" , "Brusque - lawyer (slang)" .)