BA 339 then BA 213 at Heathrow
Nice → London → Boston
Timetable, London time
12:25BA 339 from Nice at the gate
11:40BA 213 to Boston leaves the gate
23 h 15 apart on the timetable, overnight
BA 213 leaves 23 h 15 after BA 339 arrives on the timetable: more than half a day, so not a connection we count.