AA 2143 then AA 1776 at Boston
Chicago O'Hare → Boston → Philadelphia
Timetable, Boston time
11:59AA 2143 from Chicago O'Hare at the gate
16:01AA 1776 to Philadelphia leaves the gate
4 h 02 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 2143 and AA 1776 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.