UA 3874 then AA 391 at O'Hare
Chicago Rockford → Chicago → Dallas-Fort Worth
Timetable, Chicago time
01:21UA 3874 from Chicago Rockford at the gate
13:46AA 391 to Dallas-Fort Worth leaves the gate
12 h 25 apart on the timetable
AA 391 leaves 12 h 25 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.