title: get DateTime.UtcNow.Ticks older than a day
body: <p>I am saving images with unique names. To get unique name I used <code>DateTime.UtcNow.Ticks</code>. Now I want to delete all images older than a day. How can I get the ticks older than a day? 
  I have mapped time with ticks. </p>
  
  <pre><code>1:52:14.312 PM - 633614215343125000
  1:52:14.359 PM - 633614215343593750
  1:52:14.421 PM - 633614215344218750
  1:52:14.468 PM - 633614215344687500
  1:52:14.515 PM - 633614215998593750
  </code></pre>
  
  <p>What is the best way to get ticks older than a day? OR how to get the ticks of 24 hours ago?</p>