AA 2748 then UA 3376 at O'Hare
Las Vegas → Chicago → St Louis
Timetable, Chicago time
20:07AA 2748 from Las Vegas at the gate
11:00UA 3376 to St Louis leaves the gate
14 h 53 apart on the timetable, overnight
UA 3376 leaves 14 h 53 after AA 2748 arrives on the timetable: more than half a day, so not a connection we count.