UA 3874 then AA 846 at O'Hare
Chicago → Chicago → Phoenix
Timetable, Chicago time
01:21UA 3874 from Chicago at the gate
21:30AA 846 to Phoenix leaves the gate
20 h 09 apart on the timetable
AA 846 leaves 20 h 09 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.