FR 4584 then FR 7808 at Barcelona
Porto → Barcelona → London Luton
Timetable, Barcelona time
18:35FR 4584 from Porto at the gate
12:45FR 7808 to London Luton leaves the gate
18 h 10 apart on the timetable, overnight
FR 7808 leaves 18 h 10 after FR 4584 arrives on the timetable: more than half a day, so not a connection we count.