AA 3300 then UA 3376 at O'Hare
Denver → Chicago → St Louis
Timetable, Chicago time
11:45AA 3300 from Denver at the gate
11:00UA 3376 to St Louis leaves the gate
23 h 15 apart on the timetable, overnight
UA 3376 leaves 23 h 15 after AA 3300 arrives on the timetable: more than half a day, so not a connection we count.