AA 9866 then UA 5877 at O'Hare
Marquette → Chicago → Omaha
Timetable, Chicago time
10:30AA 9866 from Marquette at the gate
10:29UA 5877 to Omaha leaves the gate
23 h 59 apart on the timetable, overnight
UA 5877 leaves 23 h 59 after AA 9866 arrives on the timetable: more than half a day, so not a connection we count.