Highchart - Affichage des Données JSON - MYSQL / PHP

J'essaie d'afficher les DONNÉES JSON dans un Highchart (http://highcharts.com)

Le problème, les données pour les xAxis. Je suis vraiment confus comment obtenir le format de la date, de sorte qu'il est affiché dans la xAxis.

J'ai découvert que j'ai pour convertir la date des données de la DB à quelques millisecondes.

Quelqu'un a une idée de comment réaliser cela?

C'est mon javascript:

    var chart;

 chart = new Highcharts.Chart({
    chart: {
            renderTo: 'container',
            defaultSeriesType: 'spline',
            events: {
                load: requestData
            }},
    xAxis: {
         type: 'datetime'
      },
      yAxis: {
         title: {
            text: 'Value'
         },
         plotLines: [{
            value: 0,
            width: 1,
            color: '#808080'
         }]
      },

    series: [{
         name: 'Random data',
         data: []
        }]
});



function requestData() {
    $.ajax({
        url: '../controller/charter/data.php',
        datatype: "json",
        success: function(data) {

            alert(data);

            chart.series[0].setData(data);

        },
        cache: false
    });
}

C'est le PHP qui produit le JSON:

 <?php
header("Content-type: text/json");
//connect to the database
$dbhost = "localhost";
$dbuser = "cccccc";
$dbpassword = "ccccccc";
$database = "ccccccccc";
$tablename = "ccccccc";
$db = mysql_connect($dbhost, $dbuser, $dbpassword)
or die("Connection Error: " . mysql_error());

mysql_select_db($database) or die("Error conecting to db.");
$result = mysql_query("SELECT COUNT(*) AS count FROM $tablename");
$row = mysql_fetch_array($result,MYSQL_ASSOC);

$SQL = "SELECT aed,savedate FROM $tablename ORDER BY savedate";

$result = mysql_query( $SQL ) or die("Couldn?t execute query.".mysql_error());

$i=0;
while($row = mysql_fetch_array($result,MYSQL_ASSOC)) {

    $row[aed] = (int) $row[aed];

    $rows[$i]=array($row[savedate],$row[aed]);

    $i++;
}

echo json_encode($rows);

;
?>

Les données JSON:

[["2011-03-20 18:53:47",40],["2011-03-21 18:53:47",300],["2011-03-22 18:53:47",450],["2011-03-23 18:53:47",40],["2011-03-24 18:53:47",300],["2011-03-25 18:53:47",450],["2011-03-26 18:53:47",40],["2011-03-29 18:53:47",120],["2011-03-29 18:53:47",80],["2011-03-29 18:53:47",300],["2011-03-29 18:53:47",450],["2011-03-29 18:53:47",40],["2011-03-29 18:53:47",100],["2011-03-29 18:53:47",120],["2011-03-29 18:53:47",80],["2011-03-29 18:53:47",300],["2011-03-29 18:53:47",450],["2011-03-29 18:53:47",100],["2011-03-29 18:53:47",40],["2011-03-29 18:53:47",120],["2011-03-29 18:53:47",80],["2011-03-29 18:53:47",300],["2011-03-29 18:53:47",450],["2011-03-29 18:53:47",40],["2011-03-29 18:53:47",100],["2011-03-29 18:53:47",120],["2011-03-29 18:53:47",80],["2011-03-29 18:53:47",300],["2011-03-29 18:53:47",450],["2011-03-29 18:53:47",40],["2011-03-29 18:53:47",300],["2011-03-29 18:53:47",450],["2011-03-29 18:53:47",40],["2011-03-29 18:53:47",300],["2011-03-29 18:53:47",450],["2011-03-29 18:53:47",100]]