Delay pop-up for 10 seconds, only pop up once

Actually, none of the solutions posted previously work in real life, why?
because the line:

$("#various1").fancybox();

doesn’t trigger fancybox, it just binds fancybox to the selector #various1, but it still needs a click to trigger the modal/lightbox (not a popup). BTW, Gearóid’s solution has syntax errors anyway. The only real value is that they suggest the use of the jQuery cookie plugin (old site).

EDIT: (March 07, 2012) The jQuery cookie plugin home page moved here.

Steps for a working solution:

A) Load the jQuery cookie plugin (as suggested) after jQuery and fancybox js files

B) Then use this script:

<script type="text/javascript">
function openFancybox() {
    setTimeout( function() {$('#various1').trigger('click'); },20000);
}
$(document).ready(function() {
    var visited = $.cookie('visited');
    if (visited == 'yes') {
        return false;
    } else {
        openFancybox();
    }
    $.cookie('visited', 'yes', { expires: 7 });
    $('#various1').fancybox();
});
</script>

C) you still need to have somewhere in your html code (maybe hidden)

<a id="various1" href="https://stackoverflow.com/questions/8298886/path/target"></a>

or for inline content

<a id="various1" href="#target"></a>
<div style="display: none;">
 <div id="target">message to display in fancybox</div>
</div>

Also, if you use inline content and fancybox v1.3.x, check for an existing bug and workaround here

PS. fancybox is not a popup but a modal/lightbox jQuery plugin, which is a non-intrusive solution like jGrowl from a UI point of view.