Of all my audio components the Class D AGD Audion Mk3 monoblocs require very little time to "warm up," Ten minutes is all I have ever required, and even that seems like an unnecessary ritual. The tube pre feeding then requires two hours to start grooving. The DAC and CD transport also benefit from a two hour warmup. Everything but the tube pre is left on all the time except when I will be gone from the house for days or also during thunderstorms.
I will say that the Audions did require about 50 hours of play to "break in" fresh out of the box, and that of all the power amps I have owned they reveal more tellingly what is going on with components upstream of them.