title: Dynamically preventing Laravel from filling created_at field
body: <p>I have a model corresponding to a table with "created_at" and "updated_at" fields.
  The default Laravel behavior is OK for my need:</p>
  
  <ul>
  <li>automatically filling "created_at" on inserts,</li>
  <li>automatically filling "updated_at" on updates.</li>
  </ul>
  
  <p>Great, but for some reason (too long to detail here), I need <strong>in some cases</strong> to disable this feature (I mean <strong>dynamically</strong> disabling it during the code execution). </p>
  
  <p>How can I do?<br>
  Thank you in advance</p>