I am getting some new tubes for my amp, and I want to do a 24-hour burn in. How?

If you are buying from a quality tube dealer they already “burned” them in before they tested them. You should be good to go. I know with my tube preamp I like to turn on for one hour before listening or if I just start listening I know after an hour they hit their sweet spot. Bottom line enjoy the music!

450 degrees for three hours.  Bast every thirty minutes.

I never leave tube amps on unattended, preamps and other tubed equipment may be ok, never tube amp. My two 845 SET amp owner's manuals specifically state amps should not be played more than eight hours continuously. Push pulls and lower powered SET don't generally have this limitation.
Still, I never leave any tube amp unattended;  if a power tube red plates  you're going to have a nice repair bill.
I always just listen through burn in with tube amps, can be at background volumes and my attention on other things, but I'm always in room.

Sophia tubes, and forget all this...