The everyday use of a tube amp

Hello everybody,
I know this seems to be a stupid question but hey! still have to learn... I am working at home, listening to music all day long. Until now, things were like that :
Day use, SS integrated, tunrned on the morning with the radio or music server, turned off in the evening. Muted when I need to stop the music or during the meals.
In the evening, tube amp and Turntable for 2-3 hours, serious listening or during Fly tying sessions up to late night.
I will build a new system, all tube (Dodd pre and 50Wmonoblocks), so my question is:
Excepted for the tubes that I will have to change often, is there limitations leaving the system turned on 18 hours a day? I think that it is better to leave it and to mute when I need, even for an hour or so, than to turn it on-off and so several times during the day. Thank you for the help!
If you don't mind the tube bill, all the tube equipment I have bought says it sounds better after 15 - 45 minutes warmup. I have not done any rigorous testing on this, but it seems to be true. The only other issue I can think of is heat. Some tube amps put out a tremendous amount of heat, which builds up in a room over the course fo many hours of on-time.
There must be an optimal answer to this question of leaving tubes on or off but I have never been confident I have found it. In the hay day of tubes the largest numbers were used for digital applications which are less sensitive to noise than are analog applications. Thus, the data with the greatest statistics is not totally relevant.

After listening to lots of experiences opinions, I have come to believe (without really any definitive evidence other than dealers', audio engineers and serious audiophiles I have talked to) that it is best to turn amps on only once per day and turn them off before going to bed. And my most trusted, experienced source would say, when in doubt keep them on because it is the on and off cycle that makes the tubes go noisey.

Sorry, but this is the best I can do. I just know of no controlled test with data to really answer your question. But there are lots of opinions.
If the amp is Class A, depending on the tube type and the amount of heat it generates, the spring clamps that grasp the pins in the socket might wear out earlier. Replacing these sockets may or may not be expensive to replace depending on how easy it is to get to them. Sometimes they are attached to circuit boards that buried in the chassis. Owners of your model amp can best offer their experiences.
You know I see people selling 50 year old fisher amps with original tubes that test fine and sound fine,it seems to me that it was turned on and off a lot,it also seems to me many out there want to make money selling tubes.A friend of mine that has a audio store and he specializes in tube amps told me once only replace them if they burnout which rarely happens and has never happened to me over the past 12 years. Nick
well this is completely different, but similar questions have been asked regarding projector bulb usage. One poster replied that he services projector, and someone came in with a projector that had 7000 hours on the bulb before it blew. This is an unheard of number of hours. When he asked the owner how he got so many hours, the guy said he simply woke up in the morning, turned on the projector, then turned it off before he went to bed. So at least for bulbs, the on/off cycles seem to be the killer, not necessarily the number of hours on.
Thank you for answering, I will try to leave them on when needed and check the electricity after 3 months, this could be an argument too...
I would not wait for a tube to completely stop functioning before replacing it. Tubes can get dull sounding and still function. I have had this experience. Some tubes in a particular design may be more critical than others. The manufacturer may be able to tell you which. This happens with video CRT tubes also. Users wil be happy with a CRT for years, until one gets replaced and it is much brighter than all the others. They lose brightness over the years, but so slowly, you don't realize it. The net result si that when you own tubes, you end up constantly wondering if your system is going dull, and when it's time to re-tube.
Many amplifiers (Audio Research comes to mind) have a stand-by switch that cuts plate voltage when you're not listening but don't want to actually shut down the system. They also recommend you don't leave the amp in stand-by indefinately ;-) but it's a good way to keep the amp warmed up and ready to go all day without unnecessarily using a lot of AC (and a lot of A/C ;-)

If the amp doesn't have the stand-by option, I feel a happy compromise is to restrict on/off to AM/PM as some already mentioned, and maybe once during the day if one has to leave for an hour or more (never NEVER leave tube gear going in an empty house!) If you would have to shut down and warm up your system more often than that during the day, you probably won't have time for quality listening anyway. Why put mileage on the power tubes and burn up electricity for background music? -- isn't that why SS integrateds were invented?
I have the Dodd Mono 50s (which I love) and often run them 10 hours a day. They are a Class A/B design with a standby switch and they do not run particularly hot.

The tubes used are very inexpensive: the output tubes (of which there are only two total) are widely available at $10-20 apiece and the drivers (four total) are about the same ($10-15).

According to Gary Dodd, the tubes should last five years or more with "ordinary" use. I would imagine that would mean about 1000-1500 hours/yr. so you'd need to replace them around once a year with your usage. Definitely change them before they burn out as you could lose a fuse and resistor, or worse, if not. In any event, as a poster above noted, the sound will deteriorate before the tubes give out.

Good luck and enjoy,