BA 1399 then BA 1454 at Heathrow
Belfast City → London → Edinburgh
Timetable, London time
16:35BA 1399 from Belfast City at the gate
16:10BA 1454 to Edinburgh leaves the gate
23 h 35 apart on the timetable, overnight
BA 1454 leaves 23 h 35 after BA 1399 arrives on the timetable: more than half a day, so not a connection we count.