I am planning to participate in the Jinshanling Great Wall half marathon in 2017

I am looking at different companies that offer marathon packages to the Wall for 2017 but no official race date has been announced. Is the race always on the 3rd Sunday in April? Also, I assume these travel groups charter their own buses for transportation but I might have to leave Beijing on an evening flight. Most itineraries state the buses will leave at 1700. Is regular public transportation available on the day of the event with ongoing buses back to BJ. I might want to leave immediately after the event instead of waiting for my tour group to leave at 5pm. thank you for any help you may provide.