BA 483 then BA 878 at Heathrow
Barcelona → London → Bucharest
Timetable, London time
19:25BA 483 from Barcelona at the gate
18:50BA 878 to Bucharest leaves the gate
23 h 25 apart on the timetable, overnight
BA 878 leaves 23 h 25 after BA 483 arrives on the timetable: more than half a day, so not a connection we count.