BA 1391 then BA 756 at Heathrow
Belfast City → London → Basel
Timetable, London time
10:00BA 1391 from Belfast City at the gate
09:25BA 756 to Basel leaves the gate
23 h 25 apart on the timetable, overnight
BA 756 leaves 23 h 25 after BA 1391 arrives on the timetable: more than half a day, so not a connection we count.