Tube amp on/off: best practice?

I would say since you a leaving and then coming back I would power off just in case of a problem devolping and you are not there to resolve the problem.

The on/off is supposedly harder on the tubes than just leaving them on. However, a tube blowing is scary too. You are in a "no win" situation.
For that same reason I went with solid state in my office. I just leave it on all week now. If that were tubes and they were totally safe, you would still be stuck retubing once or twice a year!
Save the tubes for home or serious listening only.

I agree with the above about not leaving the room when tubes are on, they most certainly don't always go quitely.

The best advice by the tube sellers I buy from is to conserve tube life by turning the amp off. I also asked about the power up cycle as potentially leading to excessive wear on the tubes. The answer is that most amps nowadays have a soft start cycle to blunt whatever the power surge may damage. The other concern for me is that I am fond of old stock tubes which as everyone know have become scarcer and scarcer. Therefore I really do my best to preserve them.

Generally speaking, unless a tube amp has a sentry circuit that automatically shuts down tubes in the event of tube failure (very few tube amps have such a circuit), it is not a great idea to leave a tube amp unattended, as the above posters are correct - output tube failure can resemble the 4th of July in a worst-case scenario. My tube amp has a sentry circuit and I generally leave it on all day, and at times unattended, if I intend to listen at various times during the day.

Regarding the specific question of whether tube life in tube equipment is best extended by 24/7 operation or turning it on and off, this subject has been discussed in great detail in many threads. The short answer is that tube power amps should be turned off when not in use because output tubes (the big tubes) pass a lot of current, which is hard on them (cathode stripping). The answer for small-signal tubes (i.e., the little tubes found in preamps, DAC's, and the little driver and splitter tubes found in tube amps) is more complicated, but I generally advocate leaving them on 24/7. This very recent thread about two high-end preamps includes many of my thoughts on the subject, as well as those of the founders of Atma-Sphere and BAT, but you need to read through the entire thread because the discussion of how best to extend tube life is not the actual thread topic:

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1282891541&openfrom&1&4#1