FR 338 then FR 3977 at Dublin
London Luton → Dublin → Barcelona
Timetable, Dublin time
16:20FR 338 from London Luton at the gate
08:50FR 3977 to Barcelona leaves the gate
16 h 30 apart on the timetable, overnight
FR 3977 leaves 16 h 30 after FR 338 arrives on the timetable: more than half a day, so not a connection we count.