BA 349 then BA 1406 at Heathrow
Nice → London → Belfast City
Timetable, London time
21:05BA 349 from Nice at the gate
17:10BA 1406 to Belfast City leaves the gate
20 h 05 apart on the timetable, overnight
BA 1406 leaves 20 h 05 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.