I'm from Chicago, and fly out a lot.. Are you going thru O'hare or thru Midway?
I think the minimum you would need would be 2 hours, and better to schedule 3 hours in between.
At O'hare the International wing is in bldg 5, and then you go from there to 1,2,3 or 4 terminals. A shuttle runs every 15 minutes...
So you need to find out from the airplane company what terminals you are coming into. Usually a big airline like United has all their flights in the same area, except for International (remember to bring your passport).
You can request assistance as well from the airline (for handicaps) if needed.
Weather can be variable, and sometimes you can get snowed in or thunderstorms. If you need a backup place to crash, IM me and I'll send you my cell phone so you have a place to stay if you need it.
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I'm saying 2 hours minimum, because I think 1 hour is the tighest you can get from one spot to another, and usually the flight your leaving is late.... See if you can pick an airline that has frequent flights, so if you are delayed, can get standby on the next flight.
Best, Goldi