Originally Posted by aktchi

Your timing is perfectly do-able but you'll have to be well-prepared in advance as you won't have the time to figure things out at the last minutes or recover from mistakes.

(1) Figure out the nearest Blue Line station from your meeting place. We can help if you give us the meeting location. "Michigan Avenue downtown" is a bit vague for comfort and I would feel better knowing the intersection before I suggest walking to Blue Line and also which station. (Basically Michigan Avenue runs northwards, but Blue Line turns and goes northwest, so the distance between them keeps increasing.)

(2) Purchase a return ticket when you arrive. If you are not taking the train upon arrival, purchase the ticket from any CTA station (need not be Blue Line) in advance. That way, you will be able to fly past any long lines, broken machines, etc.

(3) make sure you board the train going to O'Hare and not the one coming from here.

(4) Finally, Chicago train system is operated with the laudable goal of keeping Americans in touch with their 19th century railroad roots. It will get you to O'Hare, and that's about it. You won't have a pre-assigned "spot", comfortable seats, or luggage hold. Depending on the crowd, you may get to sit or have to stand. Hold on to suitcases or they may roll around the coach. At the boarding platform, try to pre-position yourself near the from end of the train.

Good luck.