AA 1015 then AA 2779 at Boston
Washington National → Boston → Chicago O'Hare
Timetable, Boston time
12:14AA 1015 from Washington National at the gate
15:21AA 2779 to Chicago O'Hare leaves the gate
3 h 07 apart on the timetable
Boston’s board gives an arrival time for only about 59% of its flights, so many days show no gate time.
The last days
AA 1015 and AA 2779 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.