FB 851 then BA 344 at Heathrow
Sofia → London → Nice
Timetable, London time
12:10FB 851 from Sofia at the gate
11:35BA 344 to Nice leaves the gate
23 h 25 apart on the timetable, overnight
BA 344 leaves 23 h 25 after FB 851 arrives on the timetable: more than half a day, so not a connection we count.