One hour difference, but only for some dates

Question

Why between those dates I get 5,9.... and if I use another year I get 6 ???? It only happens with March and 2008... why is there an hour difference ???

<?php
 $from = '2008-03-04';
 $to = '2008-03-10';

 echo datediff($from,$to);

 $from = '2010-03-04';
 $to = '2010-03-10';

 echo datediff($from,$to);

 function datediff($from,$to)
 {
  $diff = strtotime($to) - strtotime($from);
  $diff = $diff/(60*60*24);
  return $diff;
 }
?>

Answer 1

Daylight Saving Time.