One thing I would do is, fire a call asynchronously from the client, using JavaScript. Say something like this:
<form method="post" action="settime.php" id="timeForm">
<input type="hidden" id="localTime" name="localTime" />
</form>
And in the JavaScript:
document.getElementById("localTime").value =
(new Date()).getDate() + "/" +
(new Date()).getMonth() + "/" +
(new Date()).getYear() + " " +
(new Date()).getHours() + ":" +
(new Date()).getMinutes() + ":" +
(new Date()).getSeconds();
document.getElementById("timeForm").submit();
In the server side, you need to do something like this:
<?php
$localTime = strtotime($_POST["localTime"]);
// Do something with PHP
?>