title: Get data where DateTime is a 15m interval
body: <p>I currently have an Entry model defined similar to this:</p>
  
  <pre><code>    field :var_name, type: String
      field :var_data, type: String
      field :var_date, type: DateTime
  </code></pre>
  
  <p>I have data generated throughout the day, and have been asked to return a report of data at 15 min intervals. All the entries where the DataTime field var_date is at 15 minute intervals of the hours.  i.e 12:00  12:15  12:30  12:45 </p>
  
  <p>I have a feeling this is might be simple but having a tough time at the moment with it, could anyone please help.</p>
  
  <p>Some example data in the var_date I have is like this:</p>
  
  <pre><code>    2014-09-18T05:00:00+00:00
      2014-09-18T05:05:00+00:00
      2014-09-18T05:10:00+00:00
      2014-09-18T05:15:00+00:00
      2014-09-18T05:20:00+00:00
      2014-09-18T05:25:00+00:00
  </code></pre>