BA 1399 then BA 1352 at Heathrow
Belfast City → London → Saint Helier
Timetable, London time
15:35BA 1399 from Belfast City at the gate
15:00BA 1352 to Saint Helier leaves the gate
23 h 25 apart on the timetable, overnight
BA 1352 leaves 23 h 25 after BA 1399 arrives on the timetable: more than half a day, so not a connection we count.