How long it take before your system/amps sound

24/7 is best sound,but personally I feel guilty using any more power that absolutely necessary for eco reasons.
Not to mention that power companies are evil.

Dracule1,
I don't believe a tube DAC is going to suck up a lot of electricity, and as Tbg pointed out, turning the tubes off and on may actually shorten tube life. Tube power amps are a totally different matter.

My preamp doesn't have a power button so it is on all the time (as it was intended to be) unless it is unplugged from the wall. Intially leaving a system on overnight brings out the best sonics.

In all seriousness...or maybe a little seriousness...my old Forte' 55 takes about a half hour to get the mojo. Leaving everything on all the time is simply a shameful waste about which anybody who does that should be ashamed...or at least not admit to it in public to avoid the "wasteful douchebag" moniker. Really...really? Many modern high end amp designers (Krell, D'Agostino, etc.) are taking this into account (and being forced to by new EU standards) and have some pretty hip energy saving stuff emerging, and nobody suggests leaving tube gear on.

One hour for sure, perhaps even longer. Seems to sound awesome after a few hours, but by that time my judgement has usually been impaired by a few beverages.