BA 292 then BA 634 at Heathrow
Washington → London → Athens
Timetable, London time
10:00BA 292 from Washington at the gate
09:55BA 634 to Athens leaves the gate
23 h 55 apart on the timetable, overnight
BA 634 leaves 23 h 55 after BA 292 arrives on the timetable: more than half a day, so not a connection we count.