A3 712 then BA 487 at Barcelona
Athens → Barcelona → London Heathrow
Timetable, Barcelona time
18:45A3 712 from Athens at the gate
18:30BA 487 to London Heathrow leaves the gate
23 h 45 apart on the timetable, overnight
BA 487 leaves 23 h 45 after A3 712 arrives on the timetable: more than half a day, so not a connection we count.