<?php
session_start();
$timestamp = time();
$diff = 30; //<-Time of countdown in seconds.  ie. 3600 = 1 hr. or 86400 = 1 day.

//MODIFICATION BELOW THIS LINE IS NOT REQUIRED.
$hld_diff = $diff;
if(isset($_SESSION['ts'])) {
	$slice = ($timestamp - $_SESSION['ts']);	
	$diff = $diff - $slice;
}

if(!isset($_SESSION['ts']) || $diff > $hld_diff || $diff < 0) {
	$diff = $hld_diff;
	$_SESSION['ts'] = $timestamp;
}

//Below is demonstration of output.  Seconds could be passed to Javascript.
$diff; //$diff holds seconds less than 3600 (1 hour);

$hours = floor($diff / 3600) . ' : ';
$diff = $diff % 3600;
$minutes = floor($diff / 60) . ' : ';
$diff = $diff % 60;
$seconds = $diff;


?>
<div id="strclock">Clock Here!</div>
<script type="text/javascript">
 var hour = <?php echo floor($hours); ?>
 var min = <?php echo floor($minutes); ?>
 var sec = <?php echo floor($seconds); ?>

function countdown() {
 if(sec <= 0 && min > 0) {
  sec = 59;
  min -= 1;
 }
 else if(min <= 0 && sec <= 0) {
  min = 0;
  sec = 0;
 }
 else {
  sec -= 1;
 }
 
 if(min <= 0 && hour > 0) {
  min = 59;
  hour -= 1;
 }
 
 var pat = /^[0-9]{1}$/;
 sec = (pat.test(sec) == true) ? '0'+sec : sec;
 min = (pat.test(min) == true) ? '0'+min : min;
 hour = (pat.test(hour) == true) ? '0'+hour : hour;
 
 document.getElementById('strclock').innerHTML = hour+":"+min+":"+sec;
 setTimeout("countdown()",1000);
 }
 countdown();
</script>