BA 1292 then TK 1990 at Heathrow
Washington → London → Istanbul
Timetable, London time
10:00BA 1292 from Washington at the gate
15:20TK 1990 to Istanbul leaves the gate
5 h 20 apart on the timetable
The last days
BA 1292 and TK 1990 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.