<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php
$s1 = '2009/12/27 16:13:25.848';
$s2 = '2009/12/27 16:20:03.849';
$dt1 = DateTime::createFromFormat('Y/m/d H:i:s.u', $s1);
$dt2 = DateTime::createFromFormat('Y/m/d H:i:s.u', $s2);
$dd = $dt2->diff($dt1);
$us1 = $dt1->format('u');
$us2 = $dt2->format('u');
echo $dd->format('%H:%I:%S') . "\r\n";
echo $dd->format('%H:%I:%S') . sprintf('.%03d', ($us2-$us1)/1000000). "\r\n";
?>