AA 6486 then UA 646 at O'Hare
Detroit → Chicago → Denver
Timetable, Chicago time
17:29AA 6486 from Detroit at the gate
13:30UA 646 to Denver leaves the gate
20 h 01 apart on the timetable, overnight
UA 646 leaves 20 h 01 after AA 6486 arrives on the timetable: more than half a day, so not a connection we count.