title: Time difference using strtotime
body: <p>This shouldn't be hard, but still I don't understand what is happening.</p>
  
  <pre><code>&lt;?php
      echo date( 'H:i', strtotime( '09:00' ) - strtotime( '08:00' ) ); 
      // returns 02:00 instead of 01:00
  
      echo date( 'H:i', strtotime( '18:45' ) - strtotime( '17:15' ) ); 
      // returns 02:30 instead of 01:30
  
      echo date( 'H:i', strtotime( '17:00' ) - strtotime( '09:00' ) );
      // returns 09:00 instead of 08:00
  </code></pre>
  
  <h2>What is adding the extra hour?</h2>
  
  <p>So maybe I need to add a date?</p>
  
  <pre><code>&lt;?php
      echo date( 'H:i', strtotime( '22-09-2016 17:00:00' ) - strtotime( '22-09-2016 09:00:00' ) );
      // still 09:00 instead of 08:00
  </code></pre>
  
  <h2>Some extra information</h2>
  
  <p>I am using Laravel en tested in Xampp.</p>
  
  <p>In Laravel /config/app.php <code>'timezone' =&gt; 'Europe/Amsterdam',</code></p>
  
  <p>In Xampp <code>date_default_timezone_set('Europe/Amsterdam');</code></p>
  
  <p>Still no difference.</p>
  
  <p><strike>This calculation is done in the blade template where I cannot access the DateTime class.</strike></p>
  
  <p>I found a way to use the DateTime class. Another solution was changing the timezone to <code>UTC</code>, but then all my other timestamps are wrong.</p>