Hi folks - I am looking at flights into Chicago in a couple weeks. Getting is in not the concern. However, when my meetings are done at 5:00 PM on a Friday (on Michigan Avenue downtown), I am trying to figure out the most reasonable flight time to take. As a Delta flyer, I prefer to take Delta back to MSP. However, the big issue is that Delta's last flight leaves O'Hare at 7:21 PM. How unreasonable is it hop on the Blue Line at 5:15 or so downtown, get to O'Hare, go through security, and make this flight? I assume the interstate (taxi) would be out as an option at rush hour time.
Of course, my alternative is later flights on United or American... but hey, I'm tied to Skymiles. Any thoughts?

A follow-up question: If 7:21 is unreasonable, what is the earliest reasonable departure time I should look at? I'd prefer to spend as little of my Friday as possible sitting at O'Hare waiting.