BA 961 then FI 451 at Heathrow
Hamburg → London → Reykjavík
Timetable, London time
12:20BA 961 from Hamburg at the gate
12:15FI 451 to Reykjavík leaves the gate
23 h 55 apart on the timetable, overnight
FI 451 leaves 23 h 55 after BA 961 arrives on the timetable: more than half a day, so not a connection we count.