title: How can I add two date strings in the format HH:MM:SS together?
body: <p>I am saving the variables in the format of HH:MM:SS.
  I want to sum up several variables such as: </p>
  
  <pre><code>TotalTime += var1+var2
  </code></pre>
  
  <p>It gives me the result of 0,
  whats the right format for getting the sum as HH:MM:SS?</p>