I would recommend leaving the amp on 24/7 for best results. You could save on energy by using the A- A/B selector switch. Listen in Class A, and switch to Class A/B when not listening. Otherwise, I would say that you will get 95% of the best performance at 2-3 hours warm up. 10-15 hours will get you pretty close to 100%, all in Class A bias FWIW.
Great amp BTW, about as good as SS gets.
Cheers,
John