BA 893 then BA 15 at Heathrow
Sofia → London → Sydney
Timetable, London time
21:50BA 893 from Sofia at the gate
21:00BA 15 to Sydney leaves the gate
23 h 10 apart on the timetable, overnight
BA 15 leaves 23 h 10 after BA 893 arrives on the timetable: more than half a day, so not a connection we count.