BA 613 then BA 638 at Heathrow
Tromso → London → Athens
Timetable, London time
16:40BA 613 from Tromso at the gate
16:15BA 638 to Athens leaves the gate
23 h 35 apart on the timetable, overnight
BA 638 leaves 23 h 35 after BA 613 arrives on the timetable: more than half a day, so not a connection we count.