BA 349 then BA 203 at Heathrow
Nice → London → Boston
Timetable, London time
21:05BA 349 from Nice at the gate
17:00BA 203 to Boston leaves the gate
19 h 55 apart on the timetable, overnight
BA 203 leaves 19 h 55 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.