FB 807 then BA 637 at Athens
Sofia → Athens → London Heathrow
Timetable, Athens time
19:50FB 807 from Sofia at the gate
19:40BA 637 to London Heathrow leaves the gate
23 h 50 apart on the timetable, overnight
BA 637 leaves 23 h 50 after FB 807 arrives on the timetable: more than half a day, so not a connection we count.