BA 779 then BA 638 at Heathrow
Stockholm → London → Athens
Timetable, London time
17:10BA 779 from Stockholm at the gate
16:15BA 638 to Athens leaves the gate
23 h 05 apart on the timetable, overnight
BA 638 leaves 23 h 05 after BA 779 arrives on the timetable: more than half a day, so not a connection we count.