Optimal Warm Up Time for ST 70

Acquired an ST 70 with the standard VTA board about 3 months ago. Very pleased. I allow about 30 seconds warm up before applying a signal. After about 45 minutes of listening the volume level seems to increase and/or the sound opens up. Across the spectrum just better. Is that normal for a tube amp?

Checked the bias shortly after turn on and after about an hour. Small difference, but both checks measure 0.385 - 0.400 V. Can a few milliamps impact power output?

I'm not sure what amount of time we should wait for warm up but I pretty much do as you do and give it like 30 seconds as I get something picked out to play. I believe that I read somewhere it does take some time for a tube to warm up to full temperature so it makes since to me that after some time it will get to it peak performance. I haven't noticed mine getting louder but it does sound a little better after 15 minutes or so.