UA 3874 then AA 3620 at O'Hare
Chicago Rockford → Chicago → St Louis
Timetable, Chicago time
01:21UA 3874 from Chicago Rockford at the gate
15:26AA 3620 to St Louis leaves the gate
14 h 05 apart on the timetable
AA 3620 leaves 14 h 05 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.