AJAX'e gerek olduğunu sanmıyorum. Basit bir jQuery saat fonksiyonu işe yarar.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>jclock</title>

  <script type="text/javascript" src="http://sites.google.com/site/jqueryjclockjs/jquery-1.2.1.min.js"></script>
  <script type="text/javascript" src="http://sites.google.com/site/jqueryjclockjs/jquery.jclock.js"></script>

  <script type="text/javascript">
    $(function($) {
      $('.jclock').jclock();
    });
  </script>

</head>

<body>
 
<div class="jclock"></div>

</body>
</html>