How to use ajax timer control

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C#

ASP.NET

Hi all,

I'm using ajax timer control in asp.net to develop online examination web application,

also i have fixed interval=6000 and if my page is rendering before this interval then
my time is being also constant.


this is my code....

protected void Timer1_Tick(object sender, EventArgs e)
    {
       Convert.ToDateTime(System.DateTime.Now.ToShortTimeString()).Subtract(Convert.ToDateTime(ViewState["StartTime"]) );
        + " minutes of 60";


            if (LblTimer.Text.ToString() == "01:30:00")
            {
                // do nothing
                Btnback.Visible = false;
                BtnNext.Text = "Finished";
                updateCandidateTestHistory();
            }
            else
            {

                DateTime dt = Convert.ToDateTime(ViewState["ElapsedTime"]);

                 dt = dt.AddMinutes(30);

                 ViewState["ElapsedTime"] = dt;
                }
                    string dt1;
                    dt1 = dt.TimeOfDay.ToString();


             
                LblTimer.Text = dt1.ToString();

            }
        }

If i'm clicking on button "NextQuestion" before 1 minute then value of lblTimer is not increasing.

pls Please give me any proper solution..