BA 1292 then BA 638 at Heathrow
Washington → London → Athens
Timetable, London time
10:00BA 1292 from Washington at the gate
16:15BA 638 to Athens leaves the gate
6 h 15 apart on the timetable
The last days
BA 1292 and BA 638 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.