The course for the Princess half marathon goes through both the Magic Kingdom and EPCOT.

Last year, the wheelchair participants started at 5:43 am and the runners started at 5:45.

There were 9 runner corrals (elite - then A thru H) I can't find what the time interval is between the corral start times, but I am pretty sure it is at least 3 - 5 minutes. So, the final participant would be crossing the start line at 6:15 at the earliest.

With a 3 1/2 hour time limit (which starts from the time the last participant crosses the start line) I believe EPCOT will be open by the time the last participants are finishing the race.

The second biggest impact, after the traffic, will be in getting around EPCOT until the race is over - the last part of the course is through EPCOT Future World so there are specific spots you are allowed to cross the course and you will be held on one side until there is a break in the participants.

A little inconvenient, but once the race is over, things should be pretty much normal.