MF 821 then VS 47 at Heathrow
Xiamen → London → New York JFK
Timetable, London time
06:25MF 821 from Xiamen at the gate
13:05VS 47 to New York JFK leaves the gate
6 h 40 apart on the timetable
The last days
MF 821 and VS 47 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.