How do I break in a tube amplifier?

I notice with my gear that after 30 minutes the sound starts to have better imaging and soundstage;after about 1 hour of listening the system sounds right to my ears.
I think you will know when it had broken in for you; it may translate into feet moving and other physical reaction as well;(air guitar,drumming,singing or even conducting the symphony;some type of envolvement).
Tubes are fantastic and a very fun part of this hobby just enjoy it.

I don't monitor the warmup of my tube amp because it's generally on providing background music from the moment I start my day until I can get around to doing some "active listening." I can comment of guitar tube amps though, because when I plug in to practice or record or simply try to entertain my neighbors, It really settles in after 20 minutes to a half hour or so...this with any one of a number of tube amps I currently use, and especially with a Class A amp I just bought. So there.

My tube amplifier is in a cabinet that I either leave the door open on or just remove when the amp is running. I have noticed that if I turn the amp on and leave the door shut for a few minutes it really warms up much faster.

Is this a good way to speed up the warm up process? Obviously, I don't plan to leave the door closed for a long period of time, but it seems that 5 or 10 minutes could really speed up the process of getting the amplifier closer to fully warm operating condition.

Is heating up faster significantly harder on the tubes themselves?