prep slides on panasonic st50 question

You can run the slides in any increments you want. Hours is hours, doesn't matter how you break it up (or not).

Why are you breaking it in for 100 hours?

Yep. The main reason to run the slides is to age the phosphors evenly before calibrating.

Running the slides doesn't make the panel any more resistant to IR. The only help there is that running them when not using the TV helps you blow through the first 100 hours or so hours faster, and panels tend to be more prone to IR early on. But after that period, the TV isn't any more resistant to IR than if you just used it normally for 100 or 200 hours or whatever. Just gets you to that point faster--which is a good thing IMO. With stores having 14-30 day return periods most of the time it's good to get it broken in the first week or so and have time to make sure you like the picture, aren't getting IR more than normal etc. before the return window is past.