This is an exclusive treat for guests who book through WDTC. Toontown typically opens an hour after the park, but on one day, your family can go there as soon as the park opens, and an hour before everyone else can go in. Mickey & some characters will have an opening celebration (and pick a family to help them), involving the guests. Characters will then hang out & sign autographs, etc.
You also get one early entrance pass, where you can go to Fantasyland an hour before the park opens to go on the attractions there. In March, they'll add Buzz Lightyear Astro Blasters (so I hear) to the attractions you can go on.