Concertina piece? Not now (4)

I believe the answer is:

once

'not now' is the definition.
(at one time, but not any more)

'concertina piece?' is the wordplay.
'piece?' indicates a hidden word (I've seen 'piece of' mean this).
'ONCE' is hidden in the letters of 'concertina'.

(Other definitions for once that I've seen before include "in days of yore?" , "'... bitten, twice shy'" , "A single time" , "Long ago" , "Cone (anag.)" .)

I've seen this clue in The Everyman puzzle in The Observer.

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