BA 349 then UA 928 at Heathrow
Nice → London → Chicago
Timetable, London time
21:05BA 349 from Nice at the gate
13:35UA 928 to Chicago leaves the gate
16 h 30 apart on the timetable, overnight
UA 928 leaves 16 h 30 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.