BA 1292 then BA 860 at Heathrow
Washington → London → Prague
Timetable, London time
10:00BA 1292 from Washington at the gate
16:45BA 860 to Prague leaves the gate
6 h 45 apart on the timetable
The last days
BA 1292 and BA 860 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.