AA 3546 then AA 2199 at Boston
St Louis → Boston → Miami (MIA)
Timetable, Boston time
13:44AA 3546 from St Louis at the gate
16:56AA 2199 to Miami (MIA) leaves the gate
3 h 12 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 2199 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.