BA 349 then BA 35 at Heathrow
Nice → London → Chennai
Timetable, London time
21:05BA 349 from Nice at the gate
14:10BA 35 to Chennai leaves the gate
17 h 05 apart on the timetable, overnight
BA 35 leaves 17 h 05 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.