BA 1395 then BA 484 at Heathrow
Belfast City → London → Barcelona
Timetable, London time
13:25BA 1395 from Belfast City at the gate
12:45BA 484 to Barcelona leaves the gate
23 h 20 apart on the timetable, overnight
BA 484 leaves 23 h 20 after BA 1395 arrives on the timetable: more than half a day, so not a connection we count.