AY 1337 then BA 638 at Heathrow
Helsinki → London → Athens
Timetable, London time
17:00AY 1337 from Helsinki at the gate
16:15BA 638 to Athens leaves the gate
23 h 15 apart on the timetable, overnight
BA 638 leaves 23 h 15 after AY 1337 arrives on the timetable: more than half a day, so not a connection we count.