title: Algorithm needed to calculate difference between two times
body: <p>I have an hour selection drop down <code>0-23</code> and minutes selection drop down <code>0-59</code> for <code>Start time</code> and <code>End time</code> respectively (so four controls).</p>
  
  <p>I'm looking for an algorithm to calculate time difference using these four values.</p>
  
  <p>Since they're not stored in fancy date/time selection controls, I don't think I can use any standard date/time manipulation functions.</p>
  
  <p>How do I calculate the difference between the two times?</p>