title: Change format for Duration field in django admin
body: <p>I'm using <code>django</code> <code>DurationField</code> in a model to calculate the time difference between two <code>DateTimeField</code>.</p>
  
  <p>On the admin site for that model, the field shows up like this:</p>
  
  <pre><code># short duration
  Cumulative Total time:   0:51:33
  # longer duration
  Cumulative Total time:   2 days, 3:10:21
  </code></pre>
  
  <p>Is it possible to change the format for this field to the below given format?</p>
  
  <pre><code>Cumulative Total time:   2 days, 3 hours, 10 minutes, 21 seconds
  </code></pre>