Why does it take so many hours to brea in arc preamps and amps?

I have yet to hear a tube amp that sounds as good after 5 minutes than it does after 1 hour let alone 4 hours. That I know for sure.
Currently explainable science be damned----and I love science.

Warm up is fine for correct bias to be reached and dc offsets to stabilize.

From new first power up, a few hours are fine for all caps and components to form.

But 600hrs to reach optimum sonic ability is shear voodoo, and as has been said it's just "expectation bias" or as Nelson Pass calls it " burn-in of the listener"

Cheers George 

In the final analysis all we can listen to is manipulated power. But it is manipulated power,  be certain of that.
Is it even possible to listen to precisely the same signal every time, even if we wanted to?
Conversely could we possibly hear marginal differences, even  if we wanted to?

"I have yet to hear a tube amp that sounds as good after 5 minutes than it does after 1 hour let alone 4 hours."

agree. Air, bloom and soundstage are MIA until later on, after an hour for sure. This is the sort of thing that apparently separates the mid fi troops from the rest of us.