UA 3874 then AA 3456 at O'Hare
Chicago Rockford → Chicago → Toronto Pearson
Timetable, Chicago time
01:21UA 3874 from Chicago Rockford at the gate
20:45AA 3456 to Toronto Pearson leaves the gate
19 h 24 apart on the timetable
AA 3456 leaves 19 h 24 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.