title: TypeError: cannot subtract DatetimeArray from ndarray
body: <p>I have two columns in my dataframe - Start date and Finish date (It is a timestamp ). I would like to calculate runtime by finding the difference. When I run the code below, I get the error: <code>TypeError: cannot subtract DatetimeArray from ndarray</code>. I am also unable to split the finished date column into date and time so I can calculate runtime in another manner.</p>
  <pre><code># calculate runtime 
  pd.to_datetime(df.start_date)
  pd.to_datetime(df.finish_date)
  
  diff = pd.to_datetime(df.finish_date) - pd.to_datetime(df.start_date)
  </code></pre>
  <p>This is how the dataframe looks like:
  df</p>
  <pre><code>file_name                unique_id                                      start_date                         finish_date
          
  file1         1716b94a8d8d83c8fffe4bdd14d536ae1ee9cba6bf17e6...   2020-09-03T16:18:38.929863799Z          2020-09-03T16:20:17.615093582Z
          
  file2         87ff84ab119b798312230fceb3a8730fe74669a373650a...   2020-09-03T16:26:25.075167073Z          2020-09-04T00:04:39.702686798Z
  </code></pre>
  <p>How can I -</p>
  <ol>
  <li>either find the difference between finish &amp; start date?</li>
  <li>split the columns into date &amp; time.</li>
  </ol>