计算两个日期时间差

protected void Button1_Click(object sender, EventArgs e)
    {
        DateTime dt1 = Convert.ToDateTime("2007-3-24 11:29:12");
        DateTime dt2 = Convert.ToDateTime("2007-2-24 10:29:12");
        TimeSpan ts = dt1 - dt2;

        string timespan = "相差:"
        + ts.Days.ToString() + "天"
        + ts.Hours.ToString() + "小时"
        + ts.Minutes.ToString() + "分钟"
        + ts.Seconds.ToString() + "秒";
        Label1.Text = timespan;
    }