my timer is behaving lazzyly(delaying)

please some one help me .

my app hase a timer in quiz.

but each time a event occure than timer start with a delay of approx. 2 seconds. hear is code :-             public Quiz()
        {

            time.Interval = new TimeSpan(10000000);
            time.Tick += time_Tick;
            timestart();

        }
        public void timestart()
        {
            dtTime = dtTime.AddSeconds(-dtTime.Second);
            dtTime = dtTime.AddSeconds(31);
            time.Start();
        }
        DateTime dtTime = new DateTime(System.DateTime.Now.Year, System.DateTime.Now.Month, System.DateTime.Now.Day, 12, 0, 31);

        void time_Tick(object sender, object e)
        {
            if (dtTime.Second > 0)
            {
                dtTime = dtTime.AddSeconds(-1);
                Timer.Text = dtTime.ToString("mm:ss");
            }
            else
            {
                time.Stop();
                Button_next.Visibility = Visibility.Visible;
            }
        }