BA 345 then BA 638 at Heathrow
Nice → London → Athens
Timetable, London time
16:45BA 345 from Nice at the gate
16:15BA 638 to Athens leaves the gate
23 h 30 apart on the timetable, overnight
BA 638 leaves 23 h 30 after BA 345 arrives on the timetable: more than half a day, so not a connection we count.