UA 657 then AM 402 at Dulles
Detroit → Washington → New York JFK
Timetable, Washington time
07:21UA 657 from Detroit at the gate
16:00AM 402 to New York JFK leaves the gate
8 h 39 apart on the timetable
The last days
UA 657 and AM 402 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.