AA 2720 then UA 3376 at O'Hare
Phoenix → Chicago → St Louis
Timetable, Chicago time
16:09AA 2720 from Phoenix at the gate
11:00UA 3376 to St Louis leaves the gate
18 h 51 apart on the timetable, overnight
UA 3376 leaves 18 h 51 after AA 2720 arrives on the timetable: more than half a day, so not a connection we count.