FB 851 then BA 342 at Heathrow
Sofia → London → Nice
Timetable, London time
16:55FB 851 from Sofia at the gate
09:40BA 342 to Nice leaves the gate
16 h 45 apart on the timetable, overnight
BA 342 leaves 16 h 45 after FB 851 arrives on the timetable: more than half a day, so not a connection we count.