I thought that I read because it is closing early for a cast member celebration event, they do their best to close promptly at 4:30. I think somebody mentioned that they may close the lines to popular rides like 7DMT earlier than 4:30 to give them some time to work through everybody currently in line.
I've never been there on a cast member celebration day before, but plan on being there this time. I'm hoping that most lines will be shorter than mornings on
MNSSHP or
MVMCP days.