BA 1393 then BA 678 at Heathrow
Belfast City → London → Istanbul
Timetable, London time
11:25BA 1393 from Belfast City at the gate
10:35BA 678 to Istanbul leaves the gate
23 h 10 apart on the timetable, overnight
BA 678 leaves 23 h 10 after BA 1393 arrives on the timetable: more than half a day, so not a connection we count.