I haven't understood very well what do you mean......anyway:
page1.php
<javascript>
var a=date();
document.information.dataclient.value=a;
</javascript>
<form name="information" method="POST" action="page2.php">
<input type="hidden" name="dataclient">
</form>
page2.php
<?
//$dataclient Dateofclient
//Server timedate year-month-day hour-minutes-seconds
date("Y-m-d H:i:s");
//Make difference........
?>
Something like that?