AA 642 then UA 2371 at O'Hare
Dallas-Fort Worth → Chicago → Cancún
Timetable, Chicago time
13:10AA 642 from Dallas-Fort Worth at the gate
08:40UA 2371 to Cancún leaves the gate
19 h 30 apart on the timetable, overnight
UA 2371 leaves 19 h 30 after AA 642 arrives on the timetable: more than half a day, so not a connection we count.