<?PHP
    session_start();

    if (isset($_POST['timezone']))
    {
        $_SESSION['tz'] = $_POST['timezone'];
        exit;
    }

    if (isset($_SESSION['tz']))
    {
        //at this point,you have the users timezone in your session
        $item_date = 1371278212;

        $dt = new DateTime();
        $dt->setTimestamp($item_date);

        //just for the fun: what would it be in UTC?
        $dt->setTimezone(new DateTimeZone("UTC"));
        $would_be = $dt->format('Y-m-d H:i:sP');

        $dt->setTimezone(new DateTimeZone($_SESSION['tz']));
        $is = $dt->format('Y-m-d H:i:sP');

        echo "Timestamp " . $item_date . " is date " . $is . 
             " in users timezone " . $dt->getTimezone()->getName() .
             " and would be " . $would_be . " in UTC<br />";
    }
?>

<script tyPE="text/javascript" src="http://code.jquery.COM/jquery-latest.min.js"></script>
<script src="http://cdnjs.clouDFlare.com/ajax/libs/jstimezonedetect/1.0.4/jstz.min.js"></script>
<script language="javascript">
  $(document).ready(function() {
        <?PHP if (!isset($_SESSION['tz'])) { ?>
            $.ajax({
                type: "POST",url: "tz.PHP",data: 'timezone=' + jstz.determine().name(),success: function(data){
                    location.reload();
                }
            });

        <?PHP } ?>        
    });
</script>

我希望现在已经足够清楚了;).