MbUnit features a new test decorator that asserts that the duration of the test is less than some values. DurationAttribute usage is quite intuitive as shown in the example below:

[TestFixture]
public class DurationAttributeTest
{
    [Test]
    [Duration(1,"This method succeeds (has 1 second to succeed")]
    public void EmptyMethod()
    {}

   [Test]
   [Duration(0,"This method will fail because it will  run in more that 0 seconds!")]
   public void EmptyMethodFails()
   {
      Console.WriteLine("Take your time");
   }
}