I've always turned me tube gear off when not listening to them.
I usually turn everything on and let it warm up for half an hour or more before a listening session.
I've had tube gear for so long, that out of habit, I plan when I'm going to do some serious listening, usually for a couple of hours or more, then shut everything down when I'm done.
That way I don't have to worry about constantly turning the system on and off.
Some tube preamps, like the older Audible Illusions Modulus, would keep the heaters on the tubes constantly on, even with the power turned off.
When in standby mode, peek into the preamp and see if the tubes are still glowing.
If they are, it's better to completely shut it down.
With the cost of tubes going through the roof lately, you want to get the most mileage out of them as possible.
A bigger problem with tube life is that some manufacturers run the tubes really hard, which drastically shortens their life.
CJ was infamous for this on their preamps, and would burn out preamp tubes at an alarming rate.
Some tubes are also more fragile than others, and have a much shorter life.
I've never had good tube life out of Telefunken 6DJ8's.
My Klimo Merlin would kill a pair of Telefunkens in a month.
Yet, I ran a set of Tungsram 6DJ8's in this same preamp for more than five years!