BA 391 then IB 718 at Heathrow
Brussels → London → Madrid
Timetable, London time
16:20BA 391 from Brussels at the gate
15:45IB 718 to Madrid leaves the gate
23 h 25 apart on the timetable, overnight
IB 718 leaves 23 h 25 after BA 391 arrives on the timetable: more than half a day, so not a connection we count.