<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php
$courses = json_decode('[
{"Id":1,"Navn":"A","Startdato":"\/Date(1423436400000)\/"},
{"Id":2,"Navn":"B","Startdato":"\/Date(1424041200000)\/"},
{"Id":3,"Navn":"C","Startdato":"\/Date(1424041200000)\/"}
]');

foreach ($courses as $course) {
    $dt = str_replace(array('/Date(', ')/'), array('', ''), $course->Startdato) / 1000;
    echo sprintf("Id=%d Navn=%s Startdato=%s\r\n", $course->Id, $course->Navn, date('Y-m-d H:i:s', $dt));
}
?>