FB 851 then SK 526 at Heathrow
Sofia → London → Stockholm
Timetable, London time
16:55FB 851 from Sofia at the gate
09:55SK 526 to Stockholm leaves the gate
17 h apart on the timetable, overnight
SK 526 leaves 17 h after FB 851 arrives on the timetable: more than half a day, so not a connection we count.