FB 851 then BA 139 at Heathrow
Sofia → London → Mumbai
Timetable, London time
16:45FB 851 from Sofia at the gate
09:35BA 139 to Mumbai leaves the gate
16 h 50 apart on the timetable, overnight
BA 139 leaves 16 h 50 after FB 851 arrives on the timetable: more than half a day, so not a connection we count.