AA 9866 then DL 3902 at O'Hare
Marquette → Chicago → Detroit
Timetable, Chicago time
10:30AA 9866 from Marquette at the gate
11:19DL 3902 to Detroit leaves the gate
49 min apart on the timetable
The last days
AA 9866 and DL 3902 weren’t both flown 15 min to 12 h apart in the last 21 days.
Statistics from past flights, not live flight information. Always check times and your connection with your airline, and don’t base travel or booking decisions on these numbers.