I am supposing that taking the bus to MK, then either walking over to CR or taking the resort monorail would be the best.
The 1/2 marathon is on Saturday. I just looked at the map. Mile 5 is on the road in between the CR and MK. Assuming the last group of runners leaves the start line of the 1/2 marathon by about 6:30 (first groups take off at 5:40 a.m.), even the slower runners and walkers should be clear of CR by 8 am.
I would allow extra time, because there will most likely be some traffic jams.