UA 3874 then AA 1640 at O'Hare
Chicago → Chicago → Phoenix
Timetable, Chicago time
01:21UA 3874 from Chicago at the gate
13:26AA 1640 to Phoenix leaves the gate
12 h 05 apart on the timetable
AA 1640 leaves 12 h 05 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.