Standard bebop now and then permitted flute (9)
I believe the answer is:
flageolet
'flute' is the definition.
(I've seen this before)
'standard bebop now and then permitted' is the wordplay.
'standard' becomes 'flag' (I've seen this in another clue).
'now and then' indicates alternate letters (letters taken on a regular basis, now and then).
'permitted' becomes 'let' (to let something happen is to permit it).
The alternating letters of 'bebop' are 'eo'.
'flag'+'eo'+'let'='FLAGEOLET'
(Other definitions for flageolet that I've seen before include "Blow me" , "musical instrument" , "Instrument of the recorder family" , "Type of recorder" , "Pulse" .)