UA 3874 then AA 4478 at O'Hare
Chicago Rockford → Chicago → Portland (Maine)
Timetable, Chicago time
01:21UA 3874 from Chicago Rockford at the gate
13:44AA 4478 to Portland (Maine) leaves the gate
12 h 23 apart on the timetable
AA 4478 leaves 12 h 23 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.