BA 349 then BA 135 at Heathrow
Nice → London → Mumbai
Timetable, London time
21:05BA 349 from Nice at the gate
15:05BA 135 to Mumbai leaves the gate
18 h apart on the timetable, overnight
BA 135 leaves 18 h after BA 349 arrives on the timetable: more than half a day, so not a connection we count.