You say play an iTunes playlist, you don't say on what speakers, or what device you want to play it on.
and is it an iTunes playlist that you have music stored locally for? or something you're streaming from Apple Music.
if you've got a HomePod, you can add music to a scene, but I think it only works with Apple Music. Not sure how it works if it's a playlist of your music in iTunes.
if you've got airplay speakers, (and Apple Music) it might will also work, but it airplays from one of your appleTVs, I've seen posts here about it actually turning on the TV when this happens.
The long slow fades you want to do can be accomplished with hue, BUT you'll have to code it yourself. If you understand some web tech basics, it's pretty easy to control. But you'll need the be able to send a PUT request with a JSON message to your hub. just google "Hue API"
You can send PUT requests using the shortcuts app, but you'll need to authorize beforehand
The timing like that can not be done with homekit or the hue app.
with shortcuts, you might be able to do something a little simpler, I think iOS14 made it so you can have longer delays, previously you could only do a couple minutes. That might still be the case. so you might be able to do ...
"turn lights blue"
"wait 5 minutes"
"turn off light 1"
"wait 5 minutes"
"turn off light 2"
With these, the lights will fade in their normal 1-2 seconds, but will wait before they do
and like I said, shortcuts might stop running after a couple minutes, so this might not work.
in shortcuts, you can also start a playlist on your phone, and then hand it off to a HomePod if you wanted.
