Why no “Break in” period?

Because a lot of stuff really does sound so good you notice immediately and right out of the box. Doesn't mean it doesn't continue to improve as it burns in.

Because a lot of stuff really does sound so good you notice immediately

That's called "expectation bias", and it's a beaut smoke screen, even for something you won't like in a day or so.

Cheers George

If someone does have noisy power putting in the conditioner will have an immediate impact.The noise floor will drop but doesn't mean that their won't be some other changes in sound as the unit breaks in.

As for expectation bias I suppose we all have it,but what do you call it when you get a new 'thing' and it's disappointing and doesn't meet expectations?I'm not able to deny to myself that the 'thing' I was so excited about acquiring sounds like shite.

+1 to what millercarbon said. 
 
-1 to what georghifi said.