AA 6246 then UA 3376 at O'Hare
Nashville → Chicago → St Louis
Timetable, Chicago time
19:51AA 6246 from Nashville at the gate
11:00UA 3376 to St Louis leaves the gate
15 h 09 apart on the timetable, overnight
UA 3376 leaves 15 h 09 after AA 6246 arrives on the timetable: more than half a day, so not a connection we count.