I commute to & from ORD while living on the West Coast. With that being said, I've never gotten a SAD, gotten bumped or missed a commute. Get there early enough to get the jump if needed & allow a few flights before the last one so you don't get stuck. Some people may choose to play it a little closer (commute in the morning of or the take the last flight of the day in), but you will figure out what works for you after you learn the ropes.
FYI, keep your options open on holidays, it can be a real mess.