FR 6920 then FR 340 at Dublin
Barcelona → Dublin → London Luton
Timetable, Dublin time
21:40FR 6920 from Barcelona at the gate
15:00FR 340 to London Luton leaves the gate
17 h 20 apart on the timetable, overnight
FR 340 leaves 17 h 20 after FR 6920 arrives on the timetable: more than half a day, so not a connection we count.