title: PHP DateTime timestamps are not correct
body: <p>I have a timestamp which I am trying to convert to another timezone. I need to take DST in to account when doing so.</p>
  
  <p>The code I am using is below:</p>
  
  <pre><code>    $date = new DateTime("@".$timestamp); 
  
      echo $date-&gt;format('Y-m-d H:i:s')."\r\n";
  
      $date-&gt;setTimezone(new DateTimeZone('Europe/Paris'));   
      echo $date-&gt;format('Y-m-d H:i:s')."\r\n";  // Pacific time
  
      $date-&gt;setTimezone(new DateTimeZone('Europe/Athens'));
      echo $date-&gt;format('Y-m-d H:i:s')."\r\n";  // Berlin time  
  </code></pre>
  
  <p>The output (which is correct) is:</p>
  
  <pre><code> 2014-01-30 20:24:48
   2014-01-30 21:24:48
   2014-01-30 22:24:48
  </code></pre>
  
  <p>However if I change the format to "U" which is the value used in Date() to get timestamps the following is output:</p>
  
  <pre><code>1391113488
  1391113488
  1391113488
  </code></pre>
  
  <p>Why are the timestamps not coming out with the timezone offset applied to them?</p>