The Half on Saturday is pretty much over by 10 am. I've been looking at photos and there are a few coming in still around that but if your DS is flying in that day they probably will miss it depending on when they get in. By 9 am they should all be headed to Epcot and the roads starting to open up. Hopefully someone who was out and about around 9 am this past year can tell you how the roads were.
Sunday tell them to sleep in

LOL Actually, we went to the AK in 2004 and it's were we viewed the Marathon still in progress and we were there around 11 am I think. It's foggy in my memory but by 12 noon the last of the runners were thru AK I think or close to it. We had no problem with the bus getting us there, we stayed at OKW that year. We did have to cross the course once (maybe twice) heading to DinoLand. When we went to leave we saw who we think was the last runner going thru as the bikes were following him out (i think it was a he! LOL) All in all it was very very kewl and very inspiring since it was THAT trip that got us thinking about doing races ourselves.
The races both start at 6 am. The Half (sat) has 3.5 hours to finish from crossing the start . The Full (sun) has 7 hours (think it's still 7). More info if you would like it can be found at the Wide World of Sports website and maps of the courses.
www.disneyworldsports.com
I would just plan what PS they want when they can but really we had no troubles. We book our room as soon as we can (DVC) and have had no problems.
It's a fun weekend

Though I will say this year was a bit busier then we've been used to and we've been going in January a few years now. I think because we're heading down sooner after the holidays and people from out of the country also have different holiday lengths then we do. We talked to a lovely family from Aussie (sorry need my spellchecker!) who was there because it was their summer. Way kewl for them!
Congrats to them and hope they have a wonderful, magical honeymoon. At least they don't have to worry about loud parties next door for Saturday and Sunday nights. At least Susan and I are pooped. Mom has fetching duties for those days LOL