I've never done the party before but from what I understand they actually close California Adventure. Then you have to line up again to get in before your party time. I've heard people say they get there anywhere from 15-40 minutes early to wait in the lines by the letters in front of the entrance.
As I remember it (gone every year), they close DCA, then reopen it for the Halloween Party. The line does get long, but it moves fast. I have attended the
MNSSHP at WDW and I liked the way run it there. We could go in during the day and get the wrist colored bands to keep us in the park for the Halloween event. We were able to have dinner just before the start of MNSSHP and then join the fun. We stored our costumes in a locker. Can you believe they still use the old fashion kind of keys for their lockers? You know the kind with the bright orange plastic tops. I was sooo shocked. I laughed!