BA 1393 then BA 173 at Heathrow
Belfast City → London → New York JFK
Timetable, London time
11:25BA 1393 from Belfast City at the gate
11:20BA 173 to New York JFK leaves the gate
23 h 55 apart on the timetable, overnight
BA 173 leaves 23 h 55 after BA 1393 arrives on the timetable: more than half a day, so not a connection we count.