We were there a couple of years ago during the marathon. At that time, the half and full marathon were on the same day. We noticed that Saturday was busier than it was during the week (we went to MGM that day.) However, Sunday, during the marathon, everything at Epcot was a walk on. The only hard part was getting from one side of future world to the other. There are spots were CMs are to help you cross through the race route. It was fun to watch the race. There was a lot of energy and excitement. January is a great time to go - I wouldn't avoid that weekend because of the Marathon. Weather can be sketchy, though. Bring clothes for all the seasons (including gloves and a hat!!)