This is a great question. As you may have read, I did a bias study awhile back. I would recommend running the amp for several minutes before putting any music to it. I think 2 minutes should be fine, to let the bias voltage come to some reasonable levels (like 1.7 volts). Then I would play some music, but at softer levels for about another 5 to 10 minutes. Frank may have other time suggestions, but this is how I like to do it. The bias voltage will settle in about an hour, but can vary depending on incoming voltage. Just let the tubes warm up and the caps charge and you should be good to go, using my guidelines.
On a side note, if you should accidentally shut the amp off, do not switch in on right away. Let it sit for a few minutes, then switch it on.
Have fun listening to this amp, it's detail is wonderful.
Wayner