BA 421 then BA 864 at Heathrow
Luxembourg → London → Prague
Timetable, London time
18:10BA 421 from Luxembourg at the gate
18:05BA 864 to Prague leaves the gate
23 h 55 apart on the timetable, overnight
BA 864 leaves 23 h 55 after BA 421 arrives on the timetable: more than half a day, so not a connection we count.