var timer = null;
var elapse = 1000; // this is interval - 1000 millisecond
var start = document.getElementById('clock').innerHTML.toString(); // start time
var finish = "00:00:00"; // finished time
var docTitle = document.title;

function onTimer()
{
   //stop it when the function run over 5000 millisecond
   if (start == finish) {
      timer = null;
      window.location.reload();
      return;
   }

   var hms = new String(start).split(":");
   var s = new Number(hms[2]);
   var m = new Number(hms[1]);
   var h = new Number(hms[0]);

   s -= 1;
   if (s < 0) {
      s = 59;
      m -= 1;
   }
   if (m < 0) {
      m = 59;
      h -= 1;
   }
   var ss = s < 10 ? ("0" + s) : s;
   var sm = m < 10 ? ("0" + m) : m;
   var sh = h < 10 ? ("0" + h) : h;

   start = sh + ":" + sm + ":" + ss;
   document.getElementById('clock').innerHTML = start;

   document.title = docTitle + " | Update in: " + start;

   if ( h == 0 && m < 1 ) {
      document.getElementById('clock').style.color = "red";
   }
   timer = window.setTimeout("onTimer()", elapse);
}

timer = window.setTimeout("onTimer()", elapse);