title: datetime conversion and manipulation in python
body: <p>My raw data is in CSV. I load it as a pandas dataframe and datetime fields are loaded as objects. </p>
  
  <pre><code>datetime1   22773 non-null object
  datetime2   22771 non-null object
  </code></pre>
  
  <p>Using <code>pd.to_datetime(df['datetime1'])</code> I convert it to - <code>datetime64[ns]</code>.</p>
  
  <p>But in doing so the actual value is increased by 7 hours.</p>
  
  <p>I have 2 questions - </p>
  
  <ol>
  <li><p>What is the unit <code>datetime64[ns]</code>? is it based on unix time or some other time zone?</p></li>
  <li><p>How can I subtract the 7 hours and keep the actual value but my field format is still datetime? </p></li>
  </ol>