The Toontown pre-party begins about an hour before the "official" party start time. Last year the party officially started at 6:00pm on the day we went, but we were lined up in a special queue for Toontown around 4:45 and let in to the area around 5:00pm. There are a couple of treat trails and character meet and greets with Mickey & Minnnie, Chip & Dale, Goofy, Donald, Daisy, and Pluto all in their Halloween costumes. I'd go straight for the character lines (if you're interested in meeting characters) and then do those two treat trails as the character lines got long pretty quickly.