AA 2509 then UA 3376 at O'Hare
Charlotte → Chicago → St Louis
Timetable, Chicago time
16:10AA 2509 from Charlotte at the gate
11:00UA 3376 to St Louis leaves the gate
18 h 50 apart on the timetable, overnight
UA 3376 leaves 18 h 50 after AA 2509 arrives on the timetable: more than half a day, so not a connection we count.