BA 631 then BA 762 at Heathrow
Athens → London → Basel
Timetable, London time
17:00BA 631 from Athens at the gate
16:40BA 762 to Basel leaves the gate
23 h 40 apart on the timetable, overnight
BA 762 leaves 23 h 40 after BA 631 arrives on the timetable: more than half a day, so not a connection we count.