Most power cords I've had in my system burned in within a week. I remember one specific PC, a Nordost Frey 2. I borrowed one from my dealer to audition and it was long ago burned in, so when I put it in my system, it took probably less than a day to reach optimum sound; I asked my dealer if I could just keep it and pay him and he agreed. I discovered that week that it was a "demo" cable and so I asked my dealer to get me a new one. I put the new one in my system and it sounded horrible. But after four days it opened up and sounded like the "demo" cable. I really wish there were no burnin required, but I can honestly say that with every component or wire change, there was some amount of burnin before the item reached best sound quality.
Except for the usual naysayers @ozzy, I'm enjoying your thread.