You should never turn your tube gears on as it is too risky and a tube failure could take down other componants. Make sense? of course not. Tubes in dacs are most likely small signal tubes and should last far longer then a year, so leave it on and minimise the thermal cycle of the other componants. And may powdered sugar fall upon your ears tonight!
Tube DAC Conundrum
I have the Blacknote DAC30 which has 4 tubes in it. I read that digital stuff should be left on for everyday listening, but won't that use up the tube life a lot quicker? I am willing to change the tubes every year if leaving them on all the time will get me that far, but I don't know.