AA 642 then UA 2857 at O'Hare
Dallas-Fort Worth → Chicago → Denver
Timetable, Chicago time
13:10AA 642 from Dallas-Fort Worth at the gate
10:55UA 2857 to Denver leaves the gate
21 h 45 apart on the timetable, overnight
UA 2857 leaves 21 h 45 after AA 642 arrives on the timetable: more than half a day, so not a connection we count.