title: Identify Empty Schedule blocks
body: <p>I have a query that shows all datetimes - every 30 minutes and this is matched up to a schedule.<br />
  I would like to identify the First and Last DATEDATE where the schedule is empty in each block as highlighted in my image.</p>
  <p><a href="https://i.stack.imgur.com/Rp0DX.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Rp0DX.jpg" alt="Empty Blocks" /></a></p>