First, Magic Express is the name of the bus system from the airport to the individual resort hotels.
The buses usually circulate every 20 minutes or so, and probably a bit more frequently towards the end of the night.
Might have no wait at all, might have a two-bus wait.
not sure if you know or not but if you drive a car to MK you will have to get either the monorail or ferry back to parking lot and then a tram most likely to get to your car. it is not possible to walk from parking lot to MK. just to make sure you knew this based on question asked