title: Query Firebase data using timestamps
body: <p>Here is my current data design on Firebase (data is simply a list of jsons at the "events" reference). The fields timestamp, action, and duration are fixed, and there might be more optional fields added later.</p>
  
  <pre><code>backend-7f34e
      events
          -KQ30Lc6lasdfasdfAi1URf
              action: "Get ready"
              duration: 100
              timestamp: 1472167504389
  
          -KQ30MM8Fgasdf_o10TW
              action: "Run"
              duration: 1890
              timestamp: 1472167507411
  </code></pre>
  
  <p>I need to be able to retrieve data from a timestamp range [start, end]. Do I need to use timestamp as the key? What would be a better way to structure the data?</p>