BA 4200 then EC 1704 at Madrid
Boston → Madrid → Nice
Timetable, Madrid time
08:45BA 4200 from Boston at the gatealso AY 5370, EI 5852, AA 8849
21:20EC 1704 to Nice leaves the gate
12 h 35 apart on the timetable
EC 1704 leaves 12 h 35 after BA 4200 arrives on the timetable: more than half a day, so not a connection we count.