Work a long time producing piece for the stage (5)
I believe the answer is:
opera
'piece for the stage' is the definition.
'work a long time' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'a long time' becomes 'era' (I've seen this before).
'op'+'era'='OPERA'
'producing' is the link.
(Other definitions for opera that I've seen before include "Carmen, for instance" , "Carmen, for example" , "Tosca, for example" , "Form of theatre" , "Eg, La traviata" .)