The toll plaza and parking lot for the MK is open 24/7. Hotel guests have to go through the toll plaza to get to their hotels. So if you enter before a certain time in the morning, you just watch for the open lane and proceed through.
The same is true for Epcot and Studios. Cast Members have to go through the toll plaza to get to their parking areas, so those toll plazas never close.
The only toll plaza that completely closes is Animal Kingdom.