BA 391 then BA 588 at Heathrow
Brussels → London → Milan
Timetable, London time
16:20BA 391 from Brussels at the gate
15:50BA 588 to Milan leaves the gate
23 h 30 apart on the timetable, overnight
BA 588 leaves 23 h 30 after BA 391 arrives on the timetable: more than half a day, so not a connection we count.