var datetime = new Object();
var myDate = new Object();

datetime.init = function () {
       var ServerTimeStamp = document.getElementById('test').innerText;
	   myDate = new Date(parseInt(ServerTimeStamp) * 1000 + 4000);
	   setInterval('datetime.timer()',1000);
}

datetime.timer = function () {
	myDate.setTime(myDate.getTime()+1000);
    document.getElementById('test').innerText= "Serverzeit: " + myDate;
}