title: Why DateTime.AddHours doesn't seem to work?
body: <p>I have same result 1338161400 when I do </p>
  
  <pre><code>    DateTime origin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
      DateTime date = DateTime.Parse(@"28/05/12 01:30");
      TimeSpan diff = date.ToUniversalTime() - origin;
      Console.WriteLine( (Math.Floor(diff.TotalSeconds)).ToString());
  </code></pre>
  
  <p>as well as when I use date.AddHours(-4) :</p>
  
  <pre><code>    DateTime origin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
      DateTime date = DateTime.Parse(@"28/05/12 01:30");
      date.AddHours(-4);
      TimeSpan diff = date.ToUniversalTime() - origin;
      Console.WriteLine( (Math.Floor(diff.TotalSeconds)).ToString());
  </code></pre>
  
  <p>I try to get 1338168600 like <a href="http://www.mbari.org/staff/rich/utccalc.htm" rel="noreferrer">http://www.mbari.org/staff/rich/utccalc.htm</a></p>
  
  <p>Update:</p>
  
  <p>Thanks I changed to</p>
  
  <pre><code>    DateTime origin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
      DateTime date = DateTime.Parse(@"28/05/2012 01:30");
      date = date.AddHours(-4);
      date = date.ToUniversalTime();
      TimeSpan diff = date - origin;
      Console.WriteLine((Math.Floor(diff.TotalSeconds)).ToString());  
  </code></pre>
  
  <p>But I got 1338147000 still not 1338168600 </p>