BA 851 then BA 1394 at Heathrow
Warsaw → London → Belfast City
Timetable, London time
09:05BA 851 from Warsaw at the gate
08:40BA 1394 to Belfast City leaves the gate
23 h 35 apart on the timetable, overnight
BA 1394 leaves 23 h 35 after BA 851 arrives on the timetable: more than half a day, so not a connection we count.