title: Extract hour and minutes from timestamp but keep it in datetime format
body: <p>I have a dataframe looking like this</p>
  
  <pre><code>   open  Start show Einde show
  5   NaN     11:30   NaN
  6   16:00   18:00   19:45
  7   14:30   16:30   18:15
  8   NaN     NaN      NaN
  9   18:45   20:45   22:30
  </code></pre>
  
  <p>These hours are in string format and I would like to transform them to datetime format.
  Whenever I try to use <code>pd.to_datetime(evs['open'], errors='coerce')</code> (to change one of the columns) It changes the hours to a full datetime format like this: <code>2020-04-03 16:00:00</code> with todays date. I would like to have just the hour, but still in datetime format so I can add minutes etc.</p>
  
  <p>Now when I use <code>dt.hour</code> to access the hour, it return a string and not in <code>HH:MM</code> format.</p>
  
  <p>Can someone help me out please? I'm reading in a CSV through Pandas <code>read_csv</code> but when I use the date parser I get the same problem. Ideally this would get fixed in the <code>read_csv</code> section instead of separately but at this point I'll take anything.</p>
  
  <p>Thanks!</p>