BA 555 then BA 600 at Heathrow
Rome → London → Venezia
Timetable, London time
17:35BA 555 from Rome at the gate
17:00BA 600 to Venezia leaves the gate
23 h 25 apart on the timetable, overnight
BA 600 leaves 23 h 25 after BA 555 arrives on the timetable: more than half a day, so not a connection we count.