UA 3874 then AA 4192 at O'Hare
Chicago Rockford → Chicago → Rochester (ROC)
Timetable, Chicago time
01:21UA 3874 from Chicago Rockford at the gate
17:06AA 4192 to Rochester (ROC) leaves the gate
15 h 45 apart on the timetable
AA 4192 leaves 15 h 45 after UA 3874 arrives on the timetable: more than half a day, so not a connection we count.