BA 387 then BA 488 at Heathrow
Brussels → London → Barcelona
Timetable, London time
10:00BA 387 from Brussels at the gate
16:00BA 488 to Barcelona leaves the gate
6 h apart on the timetable
The last days
BA 387 and BA 488 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.