I have put together some code to countdown to a date specified in a PHP file using the server time to calculate the time difference.

The problem is that although the countdown is displayed correctly when the page is first loaded, when the page is refreshed in the browser the counter goes to zero.

Can anyone point out where I'm going wrong?

I'm using three files: index.html, ajaxcountdown.js & servertime.php.

index.html...

Code:
<html>
<head>
<title></title>
<SCRIPT language=JavaScript src="functions.js"></SCRIPT>
</head>
<body>
<P>Countdown ends:</P>
<script src="ajaxcountdown.js"></script>
</body>
</html>
ajaxcountdown.js...

Code:
document.writeln('<span class="" style="color:#f00;font-size:39px;font-weight:bold;" id="countdowntimer"></span>');

InitiateTimer();

function UpdateTimer()
{
	TimeLeft--;
	strText = ''
	if (TimeLeft <= 0)
	{
		strText = "NOW!!!";
	}
	else
	{
		strText = parseInt(TimeLeft/86400)+ " Days "+parseInt(TimeLeft/3600%24)+ " Hours "+parseInt(TimeLeft/60%60)+ " Minutes "+parseInt(TimeLeft/1%60)+ " Seconds ";	
	}
	document.getElementById('countdowntimer').innerHTML = strText;
}
var TimeLeft = -1;
function InitiateTimer()
{
	var http;
	var http = false;
	if (window.XMLHttpRequest) { // Mozilla, Safari,...
	http = new XMLHttpRequest();
	if (http.overrideMimeType) {
	http.overrideMimeType('text/xml');
	}
	} else if (window.ActiveXObject) { // IE
	try {
	http = new ActiveXObject("Msxml2.XMLHTTP");
	} catch (e) {
	try {
	http = new ActiveXObject("Microsoft.XMLHTTP");
	} catch (e) {}
	}
	}
	if (!http) {
	alert('Agent unable to establish communication  :( ');
	return false;
	}

	http.open("GET", "servertime.php", true);
	http.onreadystatechange = function()
	{		
		if (http.readyState == 4) {
    		//var response = http.responseText; 
    		//a = response.split('\n');
    		//TimeLeft = a[1];
    		TimeLeft = http.responseText;
    		setInterval("UpdateTimer()",1000);
   	}	 
	}
	http.send(null);
}
servertime.php...

Code:
<?php
// The number of the month when the countdown ends (1-12)
$month=12;
//The number of the day when the countdown ends (1-31)
$day=5;
//The number of the year when the countdown ends (yyyy)
$year=2008;
// How do you want the countdown displayed?
// 1 = days
// 2 = hours
// 3 = minutes
// 4 = seconds
$display = 4;
// DON'T EDIT AFTER THIS LINE
// --------------------------
$target = mktime(0, 0, 0, $month, $day, $year);
$today = time ();
$difference =($target-$today);
if ($display == 1) { echo ($difference/86400); }
if ($display == 2) { echo ($difference/3600); }
if ($display == 3) { echo ($difference/60); }
if ($display == 4) { echo ($difference); }
?>
Any help will be much appreciated!