title: mongodb: query for the time period between two date fields
body: <p>If I have documents in the following schema saved in my mongoDB:</p>
  
  <pre><code>{
    createdDate: Date,
    lastUpdate: Date
  }
  </code></pre>
  
  <p>is it possible to query for documents where the period of time between creation and the last update is e.g. greater than one day?</p>