UA 3911 then AA 492 at O'Hare
Portland (Oregon) → Chicago → Cancún
Timetable, Chicago time
17:09UA 3911 from Portland (Oregon) at the gate
10:05AA 492 to Cancún leaves the gate
16 h 56 apart on the timetable, overnight
AA 492 leaves 16 h 56 after UA 3911 arrives on the timetable: more than half a day, so not a connection we count.