Spend long time producing piece of music (7)
I believe the answer is:
passage
'piece of music' is the definition.
(passage is a kind of piece of music)
'spend long time' is the wordplay.
'spend' becomes 'pass' ('pass' can be a synonym of 'spend').
'long time' becomes 'age' ('age' can be a synonym of 'long time').
'pass'+'age'='PASSAGE'
'producing' acts as a link.
(Other definitions for passage that I've seen before include "Literary extract" , "Sea/air journey" , "Section of musical or literary work" , "Piece of text or music" , "Alley - corridor" .)