title: Calculate time difference in minutes
body: <p>I'm reading a text file which has time(hours and minutes) and IP addresses. Then I want to get the time differences and do some activity for every 5 minutes. 
  Following code does not calculate the time difference.</p>
  
  <p>sample text file:</p>
  
  <pre><code>06:03 65.55.215.62
  06:04 157.56.92.152
  06:04 66.249.74.175
  06:05 173.199.116.171
  </code></pre>
  
  <p>code:</p>
  
  <pre><code>time_ip = []
  for line in open('minutes'):
      time_ip.append(line.split(' '))    
  
  df = pandas.DataFrame(time_ip)
  df['tvalue'] = df[0]
  df['delta'] = (df['tvalue']-df['tvalue'])
  </code></pre>