时间的加减

            //DateTime d2 = DateTime.UtcNow.AddMinutes(-2);
            //System.Diagnostics.Debug.WriteLine(d2.ToString());
            //System.Diagnostics.Debug.WriteLine(DateTime.UtcNow.ToString ());

            DateTime d2 = DateTime.UtcNow;
            DateTime d3 = d2.Subtract(TimeSpan.FromMinutes(2));
            System.Diagnostics.Debug.WriteLine(d2.ToString());
            System.Diagnostics.Debug.WriteLine(d3.ToString());