BA 873 then BA 420 at Heathrow
Krakow → London → Luxembourg
Timetable, London time
18:05BA 873 from Krakow at the gate
14:00BA 420 to Luxembourg leaves the gate
19 h 55 apart on the timetable, overnight
BA 420 leaves 19 h 55 after BA 873 arrives on the timetable: more than half a day, so not a connection we count.