If your AA flight takes off from ORD on time, then it should get to PEK on time. PEK ATC gets stacked up but normally long hauls coming from North America are low on fuel and do get prioritied in. If you are delayed at the ORD end--the most likely scenario--then assume you'll be late an equal amount into PEK, since due to headwinds, they can't usually make up time in the air. In this event, be proactive before you leave ORD, getting rebooked on the second flight. On some nights, there's a KE flight PEK-ICN at 01:50 arr 05:00. If you're traveling on a day when that's not operating, CZ317 (KE codeshare) flies PEK-GMP (Gimpo, the older airport that's closer to the city) at 08:20 arr 11:30. If you can't get out until next morning, you can press the airline to put you up in a hotel or take matters into your own hands and book something yourself. Unless you had a business meeting scheduled for that first morning in Seoul, any delay shouldn't be earth-shattering since at worst you'd lose a morning in Korea.