Dear friends, thank you all very much for your advice and for bringing up many points I had not thought about myself. In the end, deciding to err on the side of caution, I just booked the later flight.

We are in no rush to reach Chicago a few hours earlier. I also appreciate that in case of delay from IST and missing the first flight, AA would have to accommodate us somehow (one ticket/PNR for the whole trip), but that could also mean being sent to JKF/BOS to wait several hours for a morning flight to ORD. I mean, first few days of January are very heavy travel time and if they don't have any seats left in good flights, nothing they can do about it.

All in all, I can imagine worse fates than being bored in a lounge with beverages, computers and reading material.