BA 391 then BA 876 at Heathrow
Brussels → London → Budapest
Timetable, London time
16:15BA 391 from Brussels at the gate
15:55BA 876 to Budapest leaves the gate
23 h 40 apart on the timetable, overnight
BA 876 leaves 23 h 40 after BA 391 arrives on the timetable: more than half a day, so not a connection we count.