Javascript/PHP countdown timer stops at a certain time?

I have this code for a countdown timer. its basically a combination of PHP/Javascript countdown timer which will gets the $end_date from a Mysql table/field.

The problem is that it will stop automatically (which is unwanted) at a certain time.

For example: I set the $end_date to September 19 2013 11:30:00 AM GMT in mysql database.

the countdown starts and works fine and starts counting down as it should. However, when the countdown timer reaches September 19 2013 13:00:00 PM GMT it will stop and it will show the Times Up message! Basically it will stop working or counting down once the $end_date has been changed to 13:00:00 PM.

I cannot see anything in my code that will cause this issue. apart from this line:

if ($now < $exp_date ) {
?>

but again, this line only tells the script when to start counting and as far i can see it shouldn't stop the countdown timer to stop as long as the timer has not reached the $end_date. or am I missing something?

here is my code:

<?php 
error_reporting(E_ALL);
ini_set('display_errors', '1');
?>
<?php date_default_timezone_set('GMT'); ?>
<?php
session_start();
// Run a select query to get my letest 6 items
// Connect to the MySQL database  
include "config/connect.php";
$dynamicList = "";
$sql = "SELECT * FROM item ORDER BY id";
$query = mysqli_query($db_conx, $sql);
$productCount = mysqli_num_rows($query); // count the output amount
if ($productCount > 0) {
    while($row = mysqli_fetch_array($query, MYSQLI_ASSOC)){ 
             $id = $row["id"];
             $product_name = $row["product_name"];
             $date_added = date("Y-m-d", strtotime($row["date_added"]));
             $end_date = date("F d Y H:i:s A T", strtotime($row["end_date"]));
             $price = $row["price"];
             $dynamicList .= '<div>' . $end_date . '
      </div>';
    }
} else {
    $dynamicList = "No Records";
}
?>

<?php
$date = $end_date;
$exp_date = strtotime($date);
$now = time();

if ($now < $exp_date ) {
?>
<script>
// Count down milliseconds = server_end - server_now = client_end - client_now
var server_end = <?php echo $exp_date; ?> * 1000;
var server_now = <?php echo time(); ?> * 1000;
var client_now = new Date().getTime();
var end = server_end - server_now + client_now; // this is the real end time

var _second = 1000;
var _minute = _second * 60;
var _hour = _minute * 60;
var _day = _hour *24
var timer;

function showRemaining()
{
    var now = new Date();
    var distance = end - now;
    if (distance < 0 ) {
       clearInterval( timer );
       document.getElementById('countdown').innerHTML = 'EXPIRED!';

       return;
    }
    var days = Math.floor(distance / _day);
    var hours = Math.floor( (distance % _day ) / _hour );
    var minutes = Math.floor( (distance % _hour) / _minute );
    var seconds = Math.floor( (distance % _minute) / _second );

    var countdown = document.getElementById('countdown');
    countdown.innerHTML = '';
   if (days) {
        countdown.innerHTML += 'Days: ' + days + '<br />';
    }
    countdown.innerHTML += 'Hours: ' + hours+ '<br />';
    countdown.innerHTML += 'Minutes: ' + minutes+ '<br />';
    countdown.innerHTML += 'Seconds: ' + seconds+ '<br />';
}

timer = setInterval(showRemaining, 1000);
</script>
<?php
} else {
    echo "Times Up";
}
?>
<div id="countdown"></div>

any help would be greatly appreciated.