So just to be clear...My ressie is for 9:20 but we can actually get in line at 8:30? This is a relief if I'm understanding this correctly, I was worried the desserts would all be gone before my party even got seated!
We need this posted in caps in a sticky: IGNORE YOUR ADR TIME FOR THE DESSERT PARTY. The ADR system insists on treating this event like a restaurant, where you have to stagger the ADR times or the staff would die. It ought to be in the ADR system as a single timed event like HDDR or the Luau. There is only one Dessert Party per night and if you have an ADR for any time at all, you have an ADR for that night's Party. The Party is supposed to start 1 hour before Wishes although some nights people report being let in a little earlier. I would imagine it has to do with whether they are fully staffed and set up early.
Anyhow, if Wishes is at 10, the Party officially begins at 9 and could begin a little earlier. I would not recommend getting there before 8:30 just in case it doesn't start until 9; part of what you are paying for with the Party is the convenience of NOT losing the entire evening in the park standing around waiting for fireworks viewing.
Try searching over on the Disney Dining Review board for Dessert Party pictures; I know someone just added pictures in the last few days as part of their review. ETA: review by the little marla, title starts " I fell off the ice cream truck", page 7. And there are lots of others, too.