BA 873 then BA 1402 at Heathrow
Krakow → London → Belfast City
Timetable, London time
18:05BA 873 from Krakow at the gate
15:55BA 1402 to Belfast City leaves the gate
21 h 50 apart on the timetable, overnight
BA 1402 leaves 21 h 50 after BA 873 arrives on the timetable: more than half a day, so not a connection we count.