This function returns an array of timestamp corresponding to Dutch National holidays. Liberation Day (Bevrijdingsdag) is added as a National holiday once every five years (2000, 2005, 2010, ...).
<?php
function getHolidays($year = null) {
    if ($year === null) {
        $year = intval(date('Y'));
    }
    
    $easterDate  = easter_date($year);
    $easterDay   = date('j', $easterDate);
    $easterMonth = date('n', $easterDate);
    $easterYear   = date('Y', $easterDate);
  
    $holidays = array(
        mktime(0, 0, 0, 1,  1,  $year),  
        mktime(0, 0, 0, 12, 25, $year),  
        mktime(0, 0, 0, 12, 26, $year)
    );
      
    if (($year % 5) == 0) {
        $holidays[] = mktime(0, 0, 0, 5, 5, $year);  
    }
    
    if ($year <= 2013) { if (date('w', mktime(0, 0, 0, 4, 30, $year)) == 0) { $holidays[] = mktime(0, 0, 0, 4, 29, $year);  } else {
            $holidays[] = mktime(0, 0, 0, 4, 30, $year);  }
    } else { if (date('w', mktime(0, 0, 0, 4, 27, $year)) == 0) { $holidays[] = mktime(0, 0, 0, 4, 26, $year);  } else {
            $holidays[] = mktime(0, 0, 0, 4, 27, $year);  }
    }
    
    $holidays[] = strtotime('-2 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    $holidays[] = mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear);
    $holidays[] = strtotime('+1 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    $holidays[] = strtotime('+39 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    $holidays[] = strtotime('+49 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    $holidays[] = strtotime('+50 days', mktime(0, 0, 0, $easterMonth, $easterDay,  $easterYear));
    sort($holidays);
  
    return $holidays;
}
$holidays = getHolidays(2014);
foreach ($holidays as $holiday) {
    echo date('d-M-Y', $holiday) . '<br>';
}
?>