I've never had problems finding parking or taking the bus to HDD.
From OKW, take Bonnet Creek Pkwy (road with OKW, POFQ/POR) north and turn left at the end of the road onto Vista Blvd. FW will be on your right about 1/2 mile.
Parking will be at the Ft Wilderness Outpost guest parking lot. Then take the bus from there to the "Settlement", where Pioneer Hall and HDD is located.
If you come via the MK Main Gate, keep to the far right and tell the parking lot CM that you are going to HDD. They'll wave you through and you'll make the next right onto Vista Blvd. FW will be on your left about 3/4 mile.
Since HDD is prepaid and tables are pre-assigned, there is no need to get there extra early. I would allow 30-40 mins for travel (10 mins by car, 10 mins waiting for bus, 10 mins to Pioneer Hall).
HTH, Steve