BA 681 then BA 632 at Heathrow
Istanbul → London → Athens
Timetable, London time
09:50BA 681 from Istanbul at the gate
09:30BA 632 to Athens leaves the gate
23 h 40 apart on the timetable, overnight
BA 632 leaves 23 h 40 after BA 681 arrives on the timetable: more than half a day, so not a connection we count.