AA 3312 then UA 3376 at O'Hare
Las Vegas → Chicago → St Louis
Timetable, Chicago time
15:53AA 3312 from Las Vegas at the gate
11:00UA 3376 to St Louis leaves the gate
19 h 07 apart on the timetable, overnight
UA 3376 leaves 19 h 07 after AA 3312 arrives on the timetable: more than half a day, so not a connection we count.