BA 391 then BA 135 at Heathrow
Brussels → London → Mumbai
Timetable, London time
16:15BA 391 from Brussels at the gate
15:05BA 135 to Mumbai leaves the gate
22 h 50 apart on the timetable, overnight
BA 135 leaves 22 h 50 after BA 391 arrives on the timetable: more than half a day, so not a connection we count.