rule of thumb: how long do you leave a tube preamp on versus turning it off then back on?

after burn in (Brent Jesse advised 60 hours on, no signal needed)

then: on, 20 minutes, magic, off. preamp and amp 

Nobody leaves tube on turn on 1/2 hour before listing.HELLO!!

Good grief! You are fortunate to own this level of gear-enjoy it. Turn it off whenever you’re done, turn on when ready to listen again...simple.

Cut back on reading audio forums to reduce neurosis.

Cut back on reading audio forums to reduce neurosis

+1

 I had a Rogue RP 7 with just four tubes so I didn't worry about this issue so much, I just turned it on when I began to listen then off at the end of the evening

so do the same thing with the AR.

I don’t think a question about preserving the tubes is neurotic at all. It’s a simple question which aims at good habits to preserve a resource.

Without over-thinking it, the better you match your listening time with the time the tubes are on, the longer they’ll last. That will give you the confidence to spend more on better tubes, rather than changing them out more often. If you find that estimating this is a pain, then just turn them on and forget the conservation thing; you'll get more pleasure that way.