Display Session (Timeout) Expire message 5 seconds before Session expire in ASP.Net

Using this code i want to show an modal pop up to the user that "your session will be expired within 5 minutes , Click here [BUTTON] to reset your session" , here's my code :

  <asp:Button ID="btnReset" Text="Reset" runat="server" OnClick="ResetSession" />
<br />
Your Session will expire in <span id = "seconds"></span> seconds.
<script type="text/javascript">
    function SessionExpireAlert(timeout) {
        var seconds = timeout / 1000;
        seconds--;
     
        document.getElementById("seconds").innerHTML = seconds;
       
        setInterval(function () {
            seconds--;
            document.getElementById("seconds").innerHTML = seconds;
        }, 1000);
       
        setTimeout(function () {
            alert("Your session has expired. You will now be redirected.");
            window.location = "About.aspx";
        }, timeout);
    }
</script>

 protected void Page_Load(object sender, EventArgs e)
    {
        Session["Name"] = "Mudassar";
        SessionStateSection section = (SessionStateSection) WebConfigurationManager.GetSection("system.web/sessionState");
        int timeout = (int)section.Timeout.TotalMinutes * 1000 * 60;
        ClientScript.RegisterStartupScript(this.GetType(), "SessionAlert", "SessionExpireAlert(" + timeout + ");", true);
    }

    protected void ResetSession(object sender, EventArgs e)
    {
        string name = Session["Name"].ToString();
    }

<sessionState timeout="60" />