AA 9866 then UA 2371 at O'Hare
Marquette → Chicago → Cancún
Timetable, Chicago time
10:30AA 9866 from Marquette at the gate
08:40UA 2371 to Cancún leaves the gate
22 h 10 apart on the timetable, overnight
UA 2371 leaves 22 h 10 after AA 9866 arrives on the timetable: more than half a day, so not a connection we count.