BA 641 then BA 854 at Heathrow
Athens → London → Prague
Timetable, London time
10:10BA 641 from Athens at the gate
10:05BA 854 to Prague leaves the gate
23 h 55 apart on the timetable, overnight
BA 854 leaves 23 h 55 after BA 641 arrives on the timetable: more than half a day, so not a connection we count.