Tube amp on/off: best practice?


My main system, with a tube integrated, is in my studio where I work 10-12 hours a day, interrupted by the occasional offsite meeting or errand.

What's the best practice/rule of thumb for powering it up and down as I duck in and out of the studio? Just leave it on all day?
How long do I need to be away for it to be better to power it down?

Right now I'm firing it up and cooling it down about 3x a day, running it a total of 6-8 hours a day.
soundgasm
I was under the misconception (?) that the power cycle was hard on the tubes, shortening their lifespan.

Also, Samhar, I thought tubes just went quietly into the night...at least that's how they've failed for me so far. But yikes - is there a fire-hazard variety of tube death I don't know about too?

Thanks for your thoughts and expertise.
I had a Winged C EL34 go bad on a power amp and it looked like it was shooting sparks inside the tube. It was crazy. I'm glad I was there to cut it off immediately.
Polk432
That's how I do it.

Soundgasm
The 9 pin tubes stay on all the time in my amp and on standby in the preamp, it's been the "big" power tubes in the amp where I've had problems. The last power tube that failed, a 6C33CB, started to glow cherry red, and the one before that started arcing. I haven't had anything catch fire and don't intend to tempt fate anymore even though my amps take 1 1/2- 2+ hrs to hit their stride, "settle in" and start sounding very good, at 3+ hrs the magic really starts to happen!!!
I would say since you a leaving and then coming back I would power off just in case of a problem devolping and you are not there to resolve the problem.
The on/off is supposedly harder on the tubes than just leaving them on. However, a tube blowing is scary too. You are in a "no win" situation.
For that same reason I went with solid state in my office. I just leave it on all week now. If that were tubes and they were totally safe, you would still be stuck retubing once or twice a year!
Save the tubes for home or serious listening only.