BA 349 then BA 878 at Heathrow
Nice → London → Bucharest
Timetable, London time
21:05BA 349 from Nice at the gate
18:50BA 878 to Bucharest leaves the gate
21 h 45 apart on the timetable, overnight
BA 878 leaves 21 h 45 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.