AA 3546 then AA 2925 at Boston
St Louis → Boston → Chicago O'Hare
Timetable, Boston time
13:44AA 3546 from St Louis at the gate
19:40AA 2925 to Chicago O'Hare leaves the gate
5 h 56 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 3546 and AA 2925 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.