There's no need to search the whole forum, by the way. You can always just go directly to the thread that is devoted to all things Halloween Time and Mickey's Halloween Party -- which is the Halloween Time at DLR Superthread. There's a lot of info about MHP there (including the 3 hours leading up to the start of the party), and usually someone there can answer a question.
Just for reference about the lines at the actual party (even though I know your question was about FP before the MHP) -- the lines for many rides are on the short side at the party, and some are even walk-ons. That's one of the benefits of the party. Things like Space Mountain Ghost Galaxy and Haunted Mansion Holiday are always going to have longer lines than some other rides because they are seasonal and very popular.