UA 2840 then AA 3484 at O'Hare
Newark → Chicago → St Louis
Timetable, Chicago time
13:54UA 2840 from Newark at the gate
09:30AA 3484 to St Louis leaves the gate
19 h 36 apart on the timetable, overnight
AA 3484 leaves 19 h 36 after UA 2840 arrives on the timetable: more than half a day, so not a connection we count.