BA 591 then BA 243 at Heathrow
Venezia → London → Mexico City
Timetable, London time
13:10BA 591 from Venezia at the gate
12:45BA 243 to Mexico City leaves the gate
23 h 35 apart on the timetable, overnight
BA 243 leaves 23 h 35 after BA 591 arrives on the timetable: more than half a day, so not a connection we count.