Musician in little room is on time (7)
I believe the answer is:
cellist
'musician' is the definition.
(I know that cellist is a type of musician)
'little room is on time' is the wordplay.
'little room' becomes 'cell' (I've seen this before).
'on' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'cell'+'is'+'t'='CELLIST'
'in' acts as a link.
(Other definitions for cellist that I've seen before include "Member of orchestra" , "Musician in string section" , "Lloyd Webber?" , "Du Pre or Lloyd Weber" , "String player" .)