title: How to add timestamps in a Pandas.Series?
body: <p>I am trying to create a Pandas Series object with a timestamp field <code>start</code>:</p>
  
  <pre><code>a = pd.Series(index=['preceding_id', 'file', 'start'],  dtype=[np.int, np.str, np.datetime64], )
  </code></pre>
  
  <p>it fails with a </p>
  
  <pre><code>TypeError: data type not understood
  </code></pre>
  
  <p>Can someone explain me what I am doing wrong?<br>
  I've been looking for dates and datetime objects in pandas, but the documentation only says how to use it as index - which is not what I want... </p>
  
  <p>Thank you!</p>