Question about valves running hours

Williewonka, sorry for your bad experience with that Chinese brand, but Cayin is a well known reputable name. Their products are top notch with lots of good reviews all over the world. Doesn't mean that a product coming out of their shelves couldn't be defective, but lets assume my amplifier is all good.
I guess all of us agree that the major issue when running valves for a long long time (more than 8 hours) it's the excessive heat. And heat is what shortens the life of a valve.
As for having to wait some minutes prior to turn it On again, yesterday someone told me that it is important because of the capacitors (?). It seems they have to "discharge" or dissipate their energy before we connect the amplifier again.
Anyone with a good simple explanation about this? 

Migueca, Glad to hear Cayin are top notch.

Re usage: Tubes have been used in broadcasting 24/7, so using for more than 8 hours should not be an issue in quality built amps.

But to extend tube life a d reduce hydro bill, power down between listening sessions.

And..... enjoy ☺

Doesn't  anyone remember?Vacuum tubes powered WWII.
Doubtful equipment was on a timer and shut off after 8 hours.

That being said, it doesn't mean keep it always on, just turn it off when you're finished listening. It is a good idea to at least have the amp in an open rack  or top shelf for ventilation.

Agreed-

Heat will kill a tube.

Another pertinent question: If valves were the power support to all communications in a recent past (from tv and radio broadcast to military coms), for how long would they live? Would a valve survive more than a few hundred hours? Were they replaced many times a year? Or did the equipments have different banks of valves to switch between them? I'm curious about how people used to operate the tubes 50 years ago.