Believe the absolutely min MCT for ORD is 30 minutes. That would make this an "illegal" ticket and UA is obligated to correct the situation. Do some research of what flights you would prefer and don't worry about award livability -- that will be UA's problem to make available. Then call and point out the problem and what you think is a solution, you should be able to get your new choice of flights (BTW on that weekend, I would not go below 45 minutes and shoot for closer to one hour)

You are actually in a good position and don't worry they might try to push you to another day -- stand firm on the Sunday. No need to go into much detail how you got the present flights -- they are what they are and UA has to fix it.