BA 1399 then BA 275 at Heathrow
Belfast City → London → Las Vegas
Timetable, London time
16:35BA 1399 from Belfast City at the gate
16:05BA 275 to Las Vegas leaves the gate
23 h 30 apart on the timetable, overnight
BA 275 leaves 23 h 30 after BA 1399 arrives on the timetable: more than half a day, so not a connection we count.