BA 339 then FI 451 at Heathrow
Nice → London → Reykjavík
Timetable, London time
12:25BA 339 from Nice at the gate
12:15FI 451 to Reykjavík leaves the gate
23 h 50 apart on the timetable, overnight
FI 451 leaves 23 h 50 after BA 339 arrives on the timetable: more than half a day, so not a connection we count.