Why am i getting NaN error for this jquery code?

Question

I'm trying to calculate time difference for each of the data gotten from database but it displays NaN Instead of the time difference

$(document).ajaxError(function(event, request, settings) {
    $('#busy').hide();
    alert("Error accessing the server");
});

function getEmployeeList() {
    $('#busy').show();
    $.getJSON(serviceURL + 'getemployees.php', function(data) {
        $('#busy').hide();
         $('#employeeList li').remove();
        employees = data.items;
        $.each(employees, function(index, employee) {
            var valuestart = $("00:00:00");
            var valuestop = $("05:00:00");

            var timeStart = new Date("01/01/2007 " + valuestart).getHours();
            var timeEnd = new Date("01/01/2007 " + valuestop).getHours();

            var difference = timeEnd - timeStart;
        $('#employeeList').append('<li><a href="employeedetails.html?id=' + employee.id + '">' +
                '<img src="js/citybus.png" class="list-icon"/>' +
                '<p class="line1">' + employee.firstName + '</p>' +
                '<p class="line2">' + difference + '</p>' +
                '<span class="bubble">' + employee.managerId + '</span></a></li>');

    });

Answer 1

var valuestart = "00:00:00";
var valuestop = "05:00:00";

You're concatenating a string with an jQuery object when creating a new Date.