allocate a lot of time--as in, plan to be at the ttc by 7am and allowing an hour or more to get there.
Your usual route encompasses the first 4 miles of the course. While not all of it is on that usual route, the front runners will quickly occupy it. And depending on how corral spacing is and where the sweepers pick up will dictate how long that main road will be limited access. Because of the time of your reservation, i don't think there is an option to try to squeeze in later since you will be driving in with all the people who didn't know a race was going on. The elite runners will likely start at 5:30 (and be finished before your bbb appt), but there are 16 corrals of runners to get through and a 16 min mile pace requirement. I don't recall how far they space the corrals. If there is even 1 runner still on the road, then the traffic restrictions will be in place.
Here is a map to assist.
http://as1.wdpromedia.com/media/rundisney/pdf/wdw-marathon/2014/marathon14_map.pdf
i have perused the on line guide--cheer zone 1 is in mk and that closes at 8:15. Also, it tells folks it will take 42 minutes to get from epcot to cheer some 1 via walking to the epcot monorail and riding over. Hopefully this will provide you some perspective that your prime usual travel time (say arriving at ttc between 7:45 and 8) will be quite congested. So planning on arriving much earlier would be in your best interest.
Hth.
I have only been a participant 3x and i have found that many of us participants, while not engaging in park time during the race to try and plan strategies for getting our friends and family around the parks to various viewing locations and it is quite an endeavor. While the crowds may be more crowded earlier, leaving later would not be any better.
Hopefully someone who has btdt as a day guest has better information for you.
