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!
sid-hoff-frenchman
I leave my tube preamp on 24/7 because I have a class A solid state amp that takes a long time to sound it's best.

Power up when listening  power down when through.Depends on the tube and voltage of preamp how long they will last. Amperex is great tube jump on some today.
I have vintage radios that are over 80 years old. The tubes are original and they all work fine.  Those small signal tubes last for ages!
I also run a class A amp (Pass XA25) with a tube preamp. I have a dedicated room and music listening is a session. When I anticipate a session coming on I turn on the amp. It can cook throughout the day if needed. When time for the session I turn it off, wait a minute for the signal path to discharge, then turn preamp on, wait a minute for it to charge, then turn amp back on. The tube pre dos not take long be at capacity. Possibly too much trouble for some.

When session is spontaneous it turn equipment on in proper order and enjoy, the XA25 catches up. 
I have been using tube preamps and phono stages for a couple decades (Audio Research). Now all my equipment is ARC tube. Typically when I head down to listen to listen I turn on my equipment and then go get coffee or wash up or take the dogs out. It takes about 10 - 15 minutes for the equipment to sound great. Most tube life with turning off and on is something like 3,000 hours. That is a very long time. I no longer think about it… even for my amp.

I have had many Pass amps and preamps. They are great, particularly with the XA series amp. But if you really want a compellingly musical and emotionally involving experience tubes by a really great company is the way to go: for me ARC, Conrad Johnson, VAC… etc.