When to power off a tube amp?

So I just got new tubes for my Lyr and really don't want to damage these tubes and want them to last for as long as possible. So I had a few questions and was hoping you guys could help me, thanks.

1) Should I turn off the amp if I am going to away for like an hour or so? Would that decrease the life of my tubes more than leaving it on that whole time I am not using them?

2) Should I let my tubes warm up before using them? If so, how long should I wait?

3) Is unplugging my headphones before turning off my amp necessary?

And just a random question out of curiosity, what if you use two different tubes in a tube amp? lol.

Thank you guys, any help would be much appreciated.