The answer to this question is simple: You first have to possess Audiophile ears. Tubeophiles in the audio industry believe that tube amps clearly sound better after a 30 minute or so warmup. But they also believe that Class A solid state amps sound much better after a 30-45 minute warmup, but that’s actually true. Perhaps somewhere someone thought, oh to heck with it, let’s simply use that formula for any amp no matter the type, and voila!