EC 3749 then IB 5424 at Barcelona
Milan → Barcelona → London Heathrow
Timetable, Barcelona time
21:30EC 3749 from Milan at the gate
18:45IB 5424 to London Heathrow leaves the gatealso LL 5424, VY 7642, BA 8084
21 h 15 apart on the timetable, overnight
IB 5424 leaves 21 h 15 after EC 3749 arrives on the timetable: more than half a day, so not a connection we count.