UA 3874 then AA 3547 at O'Hare
Chicago Rockford → Chicago → St Louis
Timetable, Chicago time
01:21UA 3874 from Chicago Rockford at the gate
16:50AA 3547 to St Louis leaves the gate
15 h 29 apart on the timetable
AA 3547 leaves 15 h 29 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.