BA 349 then BA 297 at Heathrow
Nice → London → Chicago
Timetable, London time
21:05BA 349 from Nice at the gate
15:40BA 297 to Chicago leaves the gate
18 h 35 apart on the timetable, overnight
BA 297 leaves 18 h 35 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.