KL 1712 then U2 7927 at Schiphol
Luxembourg → Amsterdam → Prague
Timetable, Amsterdam time
16:00KL 1712 from Luxembourg at the gate
13:10U2 7927 to Prague leaves the gate
21 h 10 apart on the timetable, overnight
U2 7927 leaves 21 h 10 after KL 1712 arrives on the timetable: more than half a day, so not a connection we count.