UA 657 then BA 4 at Dulles
Detroit → Washington → New York JFK
Timetable, Washington time
07:21UA 657 from Detroit at the gate
17:50BA 4 to New York JFK leaves the gate
10 h 29 apart on the timetable
The last days
UA 657 and BA 4 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.