FB 851 then EI 159 at Heathrow
Sofia → London → Dublin
Timetable, London time
16:55FB 851 from Sofia at the gate
12:10EI 159 to Dublin leaves the gate
19 h 15 apart on the timetable, overnight
EI 159 leaves 19 h 15 after FB 851 arrives on the timetable: more than half a day, so not a connection we count.