AA 2509 then UA 5901 at O'Hare
Charlotte → Chicago → St Louis
Timetable, Chicago time
16:12AA 2509 from Charlotte at the gate
15:20UA 5901 to St Louis leaves the gate
23 h 08 apart on the timetable, overnight
UA 5901 leaves 23 h 08 after AA 2509 arrives on the timetable: more than half a day, so not a connection we count.