title: I want to set a calculated priority using the server timestamp provided by Firebase
body: <p>I would like to set the priority of a child using the server time stamp provided by Firebase, <code>ServerValue.TIMESTAMP</code>:</p>
  
  <pre><code>mFirebaseref.child(userid).setPriority(ServerValue.TIMESTAMP);
  </code></pre>
  
  <p>But my case is inverse. I want to set negative <code>ServerValue.TIMESTAMP</code> to move my child to the top based on time. Is it possible to do that in Firebase without using the local time stamp <code>System.CurrentTimeInMillis()</code>?</p>
  
  <p>I would like to do something like this:</p>
  
  <pre><code>mFirebaseref.child(userid).setPriority(-ServerValue.TIMESTAMP);
  </code></pre>