Choose a musical work before the end of the concert (3)
I believe the answer is:
opt
'choose' is the definition.
(both can mean to pick something)
'a musical work before the end of the concert' is the wordplay.
'a musical work' becomes 'op' (abbreviation for opus).
'before' means one lot of letters go next to another.
'the end of the' suggests the final letters.
The last letter of 'concert' is 't'.
'op'+'t'='OPT'
(Other definitions for opt that I've seen before include "Pick from pot" , "Hold in the highest esteem" , "Prefer, choose" , "Plump for" , "Decide between possibilities, choose" .)