AA 3356 then UA 3376 at O'Hare
Memphis → Chicago → St Louis
Timetable, Chicago time
16:30AA 3356 from Memphis at the gate
11:00UA 3376 to St Louis leaves the gate
18 h 30 apart on the timetable, overnight
UA 3376 leaves 18 h 30 after AA 3356 arrives on the timetable: more than half a day, so not a connection we count.