BA 1399 then BA 598 at Heathrow
Belfast City → London → Venezia
Timetable, London time
16:25BA 1399 from Belfast City at the gate
16:20BA 598 to Venezia leaves the gate
23 h 55 apart on the timetable, overnight
BA 598 leaves 23 h 55 after BA 1399 arrives on the timetable: more than half a day, so not a connection we count.