BA 423 then BA 420 at Heathrow
Málaga → London → Luxembourg
Timetable, London time
15:00BA 423 from Málaga at the gate
14:35BA 420 to Luxembourg leaves the gate
23 h 35 apart on the timetable, overnight
BA 420 leaves 23 h 35 after BA 423 arrives on the timetable: more than half a day, so not a connection we count.