Dopo il tag </head> metti questo codice:
codice:
<script language="javascript">
function time() { 
var timeNow = new Date(); 
var hours = timeNow.getHours(); 
var minutes = timeNow.getMinutes(); 
var seconds = timeNow.getSeconds(); 
var day = timeNow.getDate(); 
var month = timeNow.getMonth(); 
var year = timeNow.getYear(); 
var timeString = "" + ((hours > 12) ? hours - 12 : hours); 
timeString += ((minutes < 10) ? ":0" : ":") + minutes; 
timeString += ((seconds < 10) ? ":0" : ":") + seconds; 
timeString += (hours >= 12) ? " P.M." : " A.M."; 
document.write("BENVENUTO SU *****.COM, SONO LE " + timeString + " del " + day + " " + month + " " + year); 
} 
</script>
<body onload="time()">