UA 3499 then AA 3484 at O'Hare
El Paso → Chicago → St Louis
Timetable, Chicago time
12:29UA 3499 from El Paso at the gate
09:30AA 3484 to St Louis leaves the gate
21 h 01 apart on the timetable, overnight
AA 3484 leaves 21 h 01 after UA 3499 arrives on the timetable: more than half a day, so not a connection we count.