Open Popup after 5 seconds what am I doing wrong?

<script type="text/javascript">

        var link;
        var element;
                    t=setTimeout(openpopupFunction,5000);
        function openPopUp(url)
        {
            link = url;
            element = document.getElementById("background");
            element.style.display = "block";
            element = document.getElementById("popup");
            element.style.display = "block";

        }
</script>