BA 349 then DL 31 at Heathrow
Nice → London → Atlanta
Timetable, London time
21:05BA 349 from Nice at the gate
12:40DL 31 to Atlanta leaves the gate
15 h 35 apart on the timetable, overnight
DL 31 leaves 15 h 35 after BA 349 arrives on the timetable: more than half a day, so not a connection we count.