How can I prevent timer skips my ASP.NET project when multiples user login at a time?

protected void timer1_tick(object sender, EventArgs e)
        {
            
            if (TimeAllSecondes > 0)
            {
                TimeAllSecondes = TimeAllSecondes - 1;
                if (TimeAllSecondes < 0)
                {
                    Session["endtime"] = DateTime.Now;
                    //Session["SubjectID3"] = txtsubid.Value;
                    //Session["SubjectName3"] = txtsubname.Value;
                    mcqmethod.update_astatus(Convert.ToString(Session["empid"]), Convert.ToInt32(Session["EXAMID"]));
                    Response.Redirect("~/MCQ/students/s_thankyou.aspx");
                  
                }
            }

            TimeSpan time_Span = TimeSpan.FromSeconds(TimeAllSecondes);
            hh = time_Span.Hours;
            mm = time_Span.Minutes;
            ss = time_Span.Seconds;
            lblTimer.Text = " Your exam time is remaining :  " + hh + ":" + mm + ":" + ss + "[H:M:S]";
         

        }

 <asp:Timer ID="timer1" runat="server" Interval="1000" OnTick="timer1_tick" ></asp:Timer>