In plasma, the phosphors change characteristics during the first 100-200 hours. Probably most importantly though is that during this time period the screen seems to be more susceptible to image retention. So some like running slides during this time period because they don't have to worry about watching channels like CNN or the NFL network and it causing IR that lasts a long time. BTW, my TV has lots of hours on it, and still has IR. I have IR now from watching CNN. You can minimize or avoid it with zooming. IR is not burn in, which is permanent. IR goes away eventually and isn't seen unless you run the wipe or the area where the IR has occurred is in a very light or white part of the picture. I play video games and use my GT50 for monitor for my laptop. I just change the settings so that IR is less likely, putting the Contrast to 60 and Brightness to 50.
The Pro Settings should be unlocked under Custom. BTW, the picture settings are unique to every input. You can find a wealth of custom settings on the AVS Forums.