Timer class

I was checking the difference in performance between SqlDataReader and DataTableReader. I needed something to measure time with. I wrote a simple class Timer. It worked just fine for me; however, I find it hard to believe that .Net framework doesn’t have anything to measure time. The reason for this post is that I hope that someone can suggest a better solution to my Timer class.
Here’s there Timer class:

public class Timer
{
  long _start;
  long _stop;

  public void Start()
  {
    _start = GetTimeInMilliseconds();
  }

  public void Stop()
  {
    _stop = GetTimeInMilliseconds();
  }

  public long TimeElapsed
  {
    get { return _stop - _start; }
  }

  private long GetTimeInMilliseconds()
  {
    return DateTime.Now.Hour * 60 * 60 * 1000
      + DateTime.Now.Minute * 60 * 1000
      + DateTime.Now.Second * 1000
      + DateTime.Now.Millisecond;
  }
}

In case you’re interested in performance difference between SqlDataReader and DataTableReader. Here’re my findings:
On single CPU machine SqlDataReader was faster and it of course was expected. However, on double CPU machine DataTableReader was slightly faster and this was a pleasant surprise for me.