Both tube and solid state amps can reach a stable operating temperature in about 15 minutes. I see no reason to leave the amp on when no one is listening just to save the warmup time. The electricity alone is enough to justify this. Didn't your parents teach you to turn off the light when you leave a room? Same goes here (and probably multiplied by a small factor if your amps are like mine: BAT VK-60). Just a few years ago we were all worried about using up the earth's resources. Whatever happened to that?
If you want to speed up the warmup process, just put a space heater under the amp. Then you only need to wait five minutes.
If you want to speed up the warmup process, just put a space heater under the amp. Then you only need to wait five minutes.