If you have tickets/reservations for MK that day or park hoppers you can skip the party line and just enter in the normal line and pick up the wristband and treat bag at one of the locations within the park. We usually do that to get in a bit early and skip the crowds lined up for the party entrance.
Not sure what time people start lining up, but we've arrived around 3:15ish before and the line was already pretty long for the party entrance. Meanwhile there was no one at the regular entrance so we breezed right through.