Logic in customizing timer in java script

Question

I have an pop up dialog that appears after every one minute and in that pop up, I have a timer that count it's time starting from 1 minute, till 0. If user presses yes in the popup dialog, the modalpop is again reset to call again after one minute. My problem is that it was working fine until I have not introduced startBackCountDown() which creates a timer inside that modal popup. Can somebody please help me. I am stucked here.

    var mins = 1;
    var secs = 0;
    var timer;


    //240000-Four minutes
    // 120000- two minutes
    //60000-OneMinute
    var myVar = setInterval(function () { myTimer() }, 60000);
    function myTimer() {
        startBackCountDown();
        $("#dialog").dialog("open");

    }



    function startBackCountDown() {
        timer = setInterval('update()', 1000);
    }
    function update() {
        var timeField = document.getElementById('Showtime');
        if (secs == 0) {
            if (mins == 0) {
                timeField.innerHTML = "Time's up!";
                clearInterval(timer);
                //alert("Time's up");
                return;
            }
            mins--;
            secs = 59;
        } else {
            secs--;
        }
        if (secs < 10) {
            timeField.innerHTML = 'Time left: ' + mins + ':0' + secs;
        } else {
            timeField.innerHTML = 'Time left: ' + mins + ':' + secs;
        }
    }


    function ClearTimerValues() {
        window.clearInterval(myVar);
        clearInterval(timer);
    }

    function SetTimerValuesAgain() {
        var client_Name = '@Session["ClientFullName"]';
        var Client_Id = '@Session["Client_LoginID"]';
        $.ajax({
            type: "POST",
            contentType: "application/json; charset=utf-8",
            url: "../Account/ResetUser",
            data: "{'User_ID':'" + Client_Id + "','Client_Name':'" + client_Name + "'}",
            dataType: "json",
            success: function (data) {
                if (data.Data == '1') {
                    myVar = setInterval(function () { myTimer() }, 60000);
                    //window.clearInterval(timer);
                    mins = 1;
                    secs = 0;
                }
                else {
                    window.clearInterval(myVar);
                    window.location = "/Account/login";
                }
            },
            error: function (xhr) {
            }
        });
    }



    $(function () {
        $("#dialog").dialog({
            resizable: false,
            height: 140,
            modal: true,
            autoOpen: false,
            show: "blind",
            hide: "blind",
            buttons: {
                "Yes": function () {
                    SetTimerValuesAgain();
                    $(this).dialog("close");
                },
                "No": function () {
                    ClearTimerValues();
                    $(this).dialog("close");
                }
            }
        });
    });