Twinkling finale for virtuoso part in duet (7)
I believe the answer is:
secondo
'part in duet' is the definition.
(second part in a musical duet)
'twinkling finale for virtuoso' is the wordplay.
'twinkling' becomes 'second' (both can mean a small amount of time).
'finale for' suggests the final letters.
The final letter of 'virtuoso' is 'o'.
'second'+'o'='SECONDO'
(Other definitions for secondo that I've seen before include "Musical" , "participant in piano duet?" , "lower part" , "Part of duet" , "Work hands perform" .)