BA 54 then BA 590 at Heathrow
Johannesburg → London → Venezia
Timetable, London time
06:45BA 54 from Johannesburg at the gate
06:10BA 590 to Venezia leaves the gate
23 h 25 apart on the timetable, overnight
BA 590 leaves 23 h 25 after BA 54 arrives on the timetable: more than half a day, so not a connection we count.