Depends on which characters you want to see. Only some come out early in past parties like Seven Dwarves, Jack and Sally, etc. If you want one of them, its good to get in line after you're allowed to enter at 4-6pm and wait during regular park hours rather than
MNSSHP hours. After 6, I would say there would already be decent lines formed. This way, you have more time during the party for the other characters and attractions. Other characters still pull in a high draw, but do not come out early like Winnie the Pooh and his friends, Princesses with their Princes, etc. Then you have some like Aladdin and Abu/Genie and Jasmine. They rotate about every half hour or so. If you want both sets, you will have to wait in the same line a second time.