title: Excel numeric date encoding (UTC) to date conversion
body: <p>I can't seem to find the answers to this, I have tried multiple things - I am still very new to R.</p>
  
  <p>I have two variables in a dataset <code>Old Data</code></p>
  
  <ul>
  <li><code>Open Date</code> - num from Excel and </li>
  <li><code>Closed Date</code> - <code>POSIXct</code>, format: "2017-10-11 12:39:37"</li>
  </ul>
  
  <p>I can't get them to subtract for each line within the dataset, the conversions seem to be off</p>
  
  <p>This is what I am trying to do (without the syntax):</p>
  
  <p><code>Newdata &lt;- Newtime = (Closed Date - Open Date) from Old Data</code></p>
  
  <p>Here is the <code>dput(Old Data)</code> results:</p>
  
  <pre><code>structure(list(open_date = c(43018, 43018, 43020, 43027), close_date = c("9/9/2018 12:11:11", 
  "9/11/2018 13:21:11", "9/1/2018 14:31:41", "9/5/2018 15:44:41"
  )), class = "data.frame", row.names = c(NA, -4L))
  </code></pre>
  
  <p>Thanks in advance!</p>