At least at
Disneyland last summer, they gave specific start times for the 100m, 200m, 400m and mile in the final race instructions. So the 100 was supposed to start at 9:15, 200/400 at 9:30, etc. I think they instructed runners and parents to check in and line up around 1/2 hour in advance. That did NOT go well - we arrived at the check-in spot at 9am and were finally heading out around 11:30am. Long waits for little kids in tight spaces, very hot, no entertainment and very unclear instructions. After the race, I read that this is very unusual and that DL had trouble because they scheduled so many races in one morning for the first time.
So we're trying the WDW version during PHM and hoping it goes more smoothly! The DL Kids Races were sold out, and PHM Kids Races are not, so that should at least help a little. I'd hope we would all be finished in less than 2 hours after the official start time! Would love more information from someone who has experience with the WDW Kids' Races in the Epcot parking lot.