Best Way To Maximize Preamp Tube Life?

I would love to learn how to best maximize tube life. Tubes have a limited lifespan, of course. So when you're not listening for a time, is it best to shut everything off to preserve the "hours" left on the tube's life? OR does the act of powering off/on itself shorten tube length as well? If so, by how much? Something like "powering off/on costs 3 hrs of tube life, so taking a music break of less than 3 hours, better to just leave it powered on." Or 1 hr, or 10 minutes, 6 hours, etc? Where is the tradeoff point?

In my system FYI, I am running a Don Sachs preamp with 4 6SN7s and 1 6BY5 rectifier.  Don says the preamp is only running the tubes at 40% of their rating. I would greatly appreciate some input from people with tube knowledge. Thanks in advance!
invalid, there are many who think SS electronics sound better.

Transistors can also have a life span especially when used in high current circuits like class A output stages. My Krell KMA 100's lasted 21 years before an output section blew. 

I use a hybrid tube phono stage. It uses three 6922s. It stays on 24/7 in standby mode. The tubes last 5-6 years and it is painfully obvious when one fails. When one does I replace all three. Three Super Low Noise 6922s cost $270.00. Having the phono stage ready to go on short notice is worth it to me. I hate waiting for anything. My Oppo Blu Ray player has been on notice since it was brand new. The transport stinks. It is painfully slow. I am forever wanting to drop kick it out the window. Anyway, 5 years is 44,000 hours. 
Pulling tubes and running a circuit without all them in there is absolutely the WRONG thing to do unless you know exactly how the circuit is designed. You can destroy a filament supply (or a tube in it), or overwork a B+ (high voltage) supply if the circuit is designed to have all the tubes in it. I have rebuilt well over 500 pieces of vintage tube gear. On some of it you can pull tubes and there is no effect, on others you better not do that except for a brief few second test on the bench to measure some voltages. If you are not using the phono section in some preamp, then get some bargain basement cheapo 12ax7 (or whatever tube it uses) and plug it in there. If you pull tubes and run things the B+ may be high due to less loading. If the circuit is poorly designed or has parts running close to their max spec, then you could see early parts failure. Again, it all depends on how the unit was designed and built. Many times I have seen things with 475 V on a 500 V rated part. You pull a tube perhaps you are now looking at 490V on that part. I don’t design or build things that way, but I have seen lots of gear that runs parts at the ragged edge. Jim McShane taught me to never run anything over about 70-75% of rating for that reason. Very good advice. You have to take into account the turn on surge as well. A lot of times your B+ may be 420V and the parts are 500V rated, but at turn on before the tubes warm up and conduct you may see 495V and then it drops. Again, if you start pulling tubes you alter that. So you darn well better know what you are dealing with before you run it without all the tubes in it. Rant over......

My experience is that a good tube circuit will sound great in 10-15 minutes after turn on. Leaving it on 24/7 buys you absolutely nothing except very poor tube life. Turning something on 2 or 3 times a day doesn’t hurt it at all unless it is very poorly designed.
Thanks to everyone who has chimed in here. Despite owning all this gear, I am not actually a gear guy - I am a music guy. I don't enjoy endlessly tinkering and swapping out equipment. What I want is the music sound that makes me smile inside and out. So once I have found the sound I love (fingers crossed!) I want to maintain it as long as possible. With tube shortages currently in all directions, including the Northern Electric 6SN7s I am running, I want to squeeze every bit of sonic joy from these tubes as possible.
Man, a fella can learn a thing or two off this forum.  If you don't want to worry about tubes forever, see if you can home audition a Pass Labs preamp, which has that inviting midrange bloom, smoothness of a tube amp, and that lit from within sound; the imaging is layered deeply, which if you like that sort of thing, is nice, but if you're say more an "old Krell" fan (before DD'Ag left) of up-front imaging where music is in the same plane as the speaker's front, then Pass is likely not a good choice.  The front ends configured in the three box set-ups are awfully good, even spanning back to the X0.2, then to the XP-30, and now the current XP-32 front end.  About the current XP front ends, I just bought the current Stereophile most recommended components issue and the XP-22 and XP-32 made the "A" List.  Have a good day all.