title: pick first date in postgreSQL
body: <p>i have a column of dates: -</p>
  <pre><code>dates
  2021-06-24 05:47:05
  2021-06-24 09:47:05
  2021-06-24 13:47:05
  2021-06-24 17:47:05
  </code></pre>
  <p>i want to pick first time of the day that is 3 hours or more than 3 hours apart from next time of the day. date is always same.</p>
  <p>expected output:-</p>
  <pre><code>2021-06-24 05:47:05
  </code></pre>