title: Add 13 hours to a timestamp
body: <p>I have a table with timestamp values like:</p>
  
  <pre>
      2009-07-14 02:00:00
  </pre>
  
  <p>I need to display them at run time with 13 hours added, like:</p>
  
  <pre>
      2009-07-14 15:00:00
  </pre>
  
  <p>What's the simplest way to do this in PHP?</p>