ContaTempo.cs

private DateTime[] StartTime;

private void ContaTempo(int i)
{

    if (StartTime[i] == DateTime.MinValue)
    {
        StartTime[i] = DateTime.Now;
    }
    else
    {
        TimeSpan ts = DateTime.Now.TimeOfDay.Subtract(StartTime[i].TimeOfDay);
        StartTime[i] = DateTime.MinValue;
        System.Diagnostics.Debug.WriteLine("Tempo:\t" + ts.ToString("mm\\:ss\\:fffffff"));
    }

}