BA 873 then BA 638 at Heathrow
Krakow → London → Athens
Timetable, London time
18:05BA 873 from Krakow at the gate
17:35BA 638 to Athens leaves the gate
23 h 30 apart on the timetable, overnight
BA 638 leaves 23 h 30 after BA 873 arrives on the timetable: more than half a day, so not a connection we count.