UA 3911 then AA 1503 at O'Hare
Portland (Oregon) → Chicago → Cancún
Timetable, Chicago time
17:09UA 3911 from Portland (Oregon) at the gate
08:25AA 1503 to Cancún leaves the gate
15 h 16 apart on the timetable, overnight
AA 1503 leaves 15 h 16 after UA 3911 arrives on the timetable: more than half a day, so not a connection we count.