Pop up time showing wrong

$(function () {
            $("#dialog").dialog({
                autoOpen: false,
                modal: true,
                title: "Session Expiration Warning",
                buttons: {
                    "Extend Session": function () {
                        ResetSession();
                    },
                    Logout: function () {
                        CloseSession();
                    },
                    Close: function () {
                        $(this).dialog('close');
                    }
                }
            });
        });
        function SessionExpireAlert(timeout) {
            var minutes = timeout / 1000/60-1;
            var seconds = 59;
            $('#seconds').html(minutes + ':' + seconds);
            var interval = setInterval(function () {

                //var timer2 = $("14:59");
                //var timer = timer2.split(':');
                //by parsing integer, I avoid all extra string processing
                //var minutes = 14;
                //var seconds = 59;
                --seconds;
                minutes = (seconds < 0) ? --minutes : minutes;
                if (minutes < 0) clearInterval(interval);
                seconds = (seconds < 0) ? 59 : seconds;
                seconds = (seconds < 10) ? '0' + seconds : seconds;
                $('#seconds').html(minutes + ':' + seconds);
            }, 1000);
            setTimeout(function () {
                //Show Popup before 900 seconds of timeout.//
                $('#dialog').dialog('open');
            }, timeout - 900 * 1000);
            setTimeout(function () {
                window.location.href = "../../../User/SessionExpired";
            }, timeout);
        };
        function ResetSession() {
            //Redirect to refresh Session.
            window.location = window.location.href;
        };
        function CloseSession() {
            //Redirect to refresh Session.//
            window.location.href = "../../../User/SessionExpired";
        };

Response.Cache.SetCacheability(HttpCacheability.NoCache);
               if (!this.IsPostBack)
               {
                   Session["Reset"] = true;
                   Configuration config = WebConfigurationManager.OpenWebConfiguration("~/Web.Config");
                   SessionStateSection section = (SessionStateSection)config.GetSection("system.web/sessionState");
                   var timeout = section.Timeout.TotalMinutes * 1000 * 60;
                   ClientScript.RegisterStartupScript(this.GetType(), "SessionAlert", "SessionExpireAlert(" + timeout + ");", true);
               }

<sessionstate mode="InProc" timeout="120">