You should cue the song right after Kylo stabs Han because it won’t really sync up if you don’t.
Actually, it’ll play while they’re talking, and then after Han gets stabbed, the duel music from Return of the Jedi will play. So, it’ll go like this:
Han and Kylo talking on bridge:
https://www.youtube.com/watch?v=52wByO_SFxA
Han after Kylo stabs him:
https://youtu.be/L63In39n86c?t=1m10s
At 1:10
And then when Chewie starts firing at stormtroopers, the music after Ben Kenobi dies in A New Hope plays:
https://youtu.be/WzU9UkVL1QA?t=8s
Kinda mirroring Luke’s reaction to Ben dying.