When to power off a tube amp?

Any tube amplifier should never be left unattended. (""More than an hour"") The tube amp could burn down your house in fifteen minutes.. I would say ten minute unattended is max if you do not like taking chances with catastrophe.
Now tube amps blowingup and starting on fire in not common. but still possible and not a good risk to leave unattended.

1-Turn off when unattended
2-Warm up is usually about 15 minutes
3-unplugging headphones is not necessary
4- Stop worrying and enjoy!

BTW, you can use different tubes as long as they are the same type!

If you go out for just an hour or so leave them on. So long as you home insurance is paid up.

Turning off is not so much the problem, it's the turn on that is the tube deteriorator in most amps.
As nearly all of them bring on the heater supply and the HT(high tension) supply immediately. That means the HT hits a cold tube.

In nearly all the tube amps I've built I bought the heaters on first with the main switch and with a 30sec auto delay circuit then the HT was connected automatically. So there wasn't a sudden shock to a cold tube with the HT.

Cheers George

I think you should have told the folks that your Lyr amp is a headphone amp. Knowing this I think that you might have gotten different responses from folks had they known.

FWIW I see no fire hazard. None. The unit supposedly runs 'hot' but that is a relative term.

I see no need to turn off the unit except on a daily basis or after you are through using the unit each day. That way it will rest at least overnight. Small tubes typically have a long life.

I would not use different brands of tubes. Brands sound different and you would have the left channel with a different tone from the right channel if you don't use the same brand & type.

Turn down the volume to minimum when you turn off the unit. That should be enuf.

Re warm up - it doesn't take much time to warm up this type of unit. 5 to 10 minutes should be enough to take off any rough edges. If it takes more you will hear why when you listen. BTW, if you replace or roll tubes, be sure to get tubes tested for low noise.