AA 9866 then AA 1503 at O'Hare
Marquette → Chicago → Cancún
Timetable, Chicago time
10:30AA 9866 from Marquette at the gate
08:25AA 1503 to Cancún leaves the gate
21 h 55 apart on the timetable, overnight
AA 1503 leaves 21 h 55 after AA 9866 arrives on the timetable: more than half a day, so not a connection we count.