Is it a OK to leave tube pre-amps powede up 24/7

I have a Rouge integrated amp with stand-by soft start. Truthfully, after a half hour warm up it sounds great and additional hours of warm up seems to make no difference, so, except for periods when I plan to listen to music for a couple of days in a row (even then usually turn on in the am and off at night unless on an all night music binge) I see no point in leaving it on 24/7. I also have a Audible Illusions Modulas II preamp, also with a stand-by soft start and left it on continually only during periods of extended listening and off during periods of not listening. I had to change out the tubes only twice in 25 years. If your pre amp has a soft start and you listen to every day, I agree with paul79, on once off once each day. 

I have a vintage CJ P-11 that's been modified.
Since I'm retired, I listen most any time of the day.
So, I leave it on all day and turn it off at night.
I used to turn it on and off and had to wait annoyingly each time I
wanted to listen to music.
I'm much happier this way, but am I doing it any harm?
i dearly love the unit.

There are only so many electrons in a vacuum tube.

There might be a limit to how many electrons can **flow** through a vacuum tube... I've seen some 6SN7s go over 50,000 hours in our gear.  Admittedly, that's an outsider number but some tubes have very long lives!

I'm much happier this way, but am I doing it any harm?

No.

Thanks for the reply

Don’t have much to add here, as about everything has been said!

For me, I turn off all of my tube gear (4 power amps and 3 preamps) when I don’t plan to listen to it within the next 2 hours. To my ears, all of my tube gear sounds great within 10-15 minutes of powering on. Some say an hour, I just don’t hear any difference of 15 minutes of warm up vs 60 minutes. The temps inside the tubes are pretty warm within 15 minutes.

I do know a guy who runs his preamps 24x7 and has for about 10 years now. Over 150,000 hours on his tubes and they still test as very good. I also know people with tube preamps from the 60s which still have their original tube sets in them - not run night & day for 50 years, but used a lot along the way - and powered on and off thousands of times. Some tubes do have very long lives!

Personally, I've never had a preamp tube burn out so I don't know how long they last.