GQ 681 then BA 631 at Athens
Sofia → Athens → London Heathrow
Timetable, Athens time
21:55GQ 681 from Sofia at the gate
14:00BA 631 to London Heathrow leaves the gate
16 h 05 apart on the timetable, overnight
BA 631 leaves 16 h 05 after GQ 681 arrives on the timetable: more than half a day, so not a connection we count.