AA 1239 then K4 578 at O'Hare
Boston → Chicago → Seoul
Timetable, Chicago time
10:30AA 1239 from Boston at the gate
07:40K4 578 to Seoul leaves the gate
21 h 10 apart on the timetable, overnight
K4 578 leaves 21 h 10 after AA 1239 arrives on the timetable: more than half a day, so not a connection we count.