title: Finding gap between date range Postgres
body: <p>I have this table and need to find gaps between intervals</p>
  
  <p>Records may be overlapping.</p>
  
  <pre><code>user |    start_time            |     end_time
  user1|2018-09-26T02:16:52.023453|2018-09-26T03:12:04.404477
  user1|2018-09-25T22:15:49.593296|2018-09-26T00:15:52.016497
  user1|2018-09-25T20:13:02.358192|2018-09-25T22:15:49.593296
  </code></pre>
  
  <p>Expected output will be </p>
  
  <pre><code> user |    start_time            |     end_time
   user1|2018-09-26T00:15:52.016497|2018-09-26T02:16:52.023453
  </code></pre>