BA 1399 then DL 37 at Heathrow
Belfast City → London → Atlanta
Timetable, London time
16:25BA 1399 from Belfast City at the gate
16:00DL 37 to Atlanta leaves the gate
23 h 35 apart on the timetable, overnight
DL 37 leaves 23 h 35 after BA 1399 arrives on the timetable: more than half a day, so not a connection we count.