title: Add new column with time only in Dataframe Pandas
body: <p>So i have this Dataframe that has been scraped from a website.What i want to achieve is to add a new column with only time in it as HH:mm each time it scrapes new data.
  But the code i use gives data and time</p>
  <pre><code>import pandas as pd 
  
  data = {'Name':['Tom', 'nick', 'krish', 'jack','Rick', 'John'],
          'Age':[20, 21, 19, 18, 26, 23]}
  df = pd.DataFrame(data) 
    
  df['time'] = pd.date_range('11/5/2020', periods = 6, freq ='2H')  
  df 
  </code></pre>
  <p>Data i have:</p>
  <pre><code>    Name    Age               time
  0   Tom     20  2020-11-05 01:00:00
  1   nick    21  2020-11-05 01:00:00
  2   krish   19  2020-11-05 01:00:00
  3   jack    18  2020-11-05 01:00:00
  4   Rick    26  2020-11-05 01:00:00
  5   John    23  2020-11-05 01:00:00
  </code></pre>
  <p>Result I want</p>
  <pre><code>    Name    Age       time
  0   Tom     20       01:00
  1   nick    21       01:00
  2   krish   19       01:00
  3   jack    18       01:00
  4   Rick    26       01:00
  5   John    23       01:00
  </code></pre>
  <p>As the data is scraped every 15 minutes I want to append the new data to it with the time without the need to add header again like below:</p>
  <pre><code>    Name    Age       time
  0   Tom     20       01:00
  1   nick    21       01:00
  2   krish   19       01:00
  3   jack    18       01:00
  4   Rick    26       01:00
  5   John    23       01:00
  0   Tom     20       01:15
  1   nick    21       01:15
  2   krish   19       01:15
  3   jack    18       01:15
  4   Rick    26       01:15
  5   John    23       01:15
  </code></pre>