Musician in little room is on time (7)
I believe the answer is:
cellist
'musician' is the definition.
(cellist is a kind of musician)
'little room is on time' is the wordplay.
'little room' becomes 'cell' (I've seen this before).
'on' says to put letters next to each other.
'time' becomes 't' (abbreviation).
'cell'+'is'+'t'='CELLIST'
'in' is the 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" .)