title: Firebase Database Rule that compares timestamp to 00:00:00 of today?
body: <p>I'm trying to create a Firebase Database Rule that forbids users to write to any node which has a timestamp created before 00:00:00 of today.</p>
  
  <p>Example of database:</p>
  
  <pre><code>{
      "messageID": { 
          "message": "blabla",
          "timestamp": 1481744636
      }
  }
  </code></pre>
  
  <p>Rules:</p>
  
  <pre><code>{
      "rules": {
          "$messageID": {
              ".write": "data.child('timestamp').val() &gt; ???"
          }
      }
  }
  </code></pre>
  
  <p>I know about the 'now' keyword, but I don't think it helps me. I need a way to compare the timestamp with a value for <code>00:00:00</code> of today. </p>
  
  <p>I could create and store a table with all the unix epoch times for midnight of each day in the futurem but isn't there a way to calculate it on the fly?</p>