DL 4995 then GF 6604 at JFK
Nashville → New York → London
Timetable, New York time
13:48DL 4995 from Nashville at the gate
21:45GF 6604 to London leaves the gate
7 h 57 apart on the timetable
The last days
DL 4995 and GF 6604 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.