Having worked in PMEL labs for over 40 years the only equipment we turned on and let stabilize was an Hewlett Packard Low Frequency Generator or oscilloscopes with CRT's the size of basketballs. The HP generator weighed in at over 400 lbs and emitted low frequency tones for calibrating. As it was in the Air Force PMEL lab which is a temperature, humidity and dust controlled environment the tubes themselves generated a tremendous amount of heat. It would actually affect the air handling system after about an hour after we turned on this bruiser. So I can see how burn in can affect tubes but not so much on small tube amps used for stereo. I would say an hour would be enough for the power supply and tubes to stabilize.
Solid state does not need to warm up. If Fluke, HP and other test equipment manufacturers said you have to warm up a piece of solid state test equipment they would be out of business.
I guess electronic theory would be the next step but that was way back in school and hole theory made my head explode. lol
Klipsch so much it Hz
OTA all the way