The last corral may start some time around 6:30, so when they're finished would depend on when they complete the race. Also, make sure they know that time spent in line for pictures counts towards your total race time so if they're slow, pictures could cause them to be swept.
If there are characters after the race and they want to get photos there, that will also impact when they arrive back at the resort. Runners can walk through Epcot afterwards, but they must have park admission to do so. Which means that if you are not planning on the parks after the race, they cannot walk back to the resort without using a park day. And if you have a 1 park per day ticket, that would lock them into Epcot for that day. Depending on where you're staying, there may be a bus from the finish line to your resort. Keep in mind that you may sit on that bus for 10-15 minutes before it leaves for the resort. And if the bus shares (Port Orleans for instance) there may be other stops before you get back to your resort.
I think a 10:00am ADR could be difficult. I finished the 2018 Dark Side 5K in just over 90 minutes from the last corral. My little sister and I made our 9:40 ADR at Be Our Guest with about 10 minutes to spare and that only happened because we didn't have to wait too long for the Magic Kingdom bus.