Hi,
It is mainly your ears getting used to the difference in sound.
I work for telex communications and Klark Teknik, where we make digital and analogue mixing desks, and sound equipment. Our stuff is burnt in for between 8 and 12 hours, to see if any of the components blow when power is surged through them, then we fully music test the compnents to see if they are in peramiters after the 8 - 12 hr period.
I agree that items with moving parts definately require time to bed down, and electrical compoents need a certain time from out of the box to get to working temp, but I really doubt about a 6 way mains block.
Like I said, the music roadies we see for all the big bands around the world, say that it is our ears that need buring into the new sound.