Good time to add notes to song (6)
I believe the answer is:
ballad
'to song' is the definition.
(ballad is a kind of song)
'good time to add notes' is the wordplay.
'good time' becomes 'ball' (I've seen this in another clue).
'to add' means one lot of letters go next to another.
'notes' becomes 'ad' (two musical notes).
'ball'+'ad'='BALLAD'
(Other definitions for ballad that I've seen before include "Narrative poem or song" , "Love song" , "Song that tells a story" , "Folk song" , "Lay, narrative song" .)