title: python: difference of two timedate strings
body: <p>I have two date strings (taken from user input and can vary greatly)</p>
  
  <pre><code>s1 = '2011:10:01:10:30:00'
  s2 = '2011:10:01:11:15:00'
  </code></pre>
  
  <p>I wish to find the difference between the two as minutes. </p>
  
  <p>How should I proceed to tackle this ?</p>