Dialog box duration setting question

Dialog box duration setting question

When I add the duration after the type of effect, the effect defaults
back to the default value but the duration works. Does anyone see the
error in the show/hide lines in the code below? Thanks
$('#dialog2').dialog({
        autoOpen: false,
        bgiframe: true,
        modal: true,
        show: ('fold', 2000),
        hide: ('fold', 500),
        width: 600,
            buttons: {
                "Yes": function() {
                    $(this).dialog("close");
                },
                "No": function() {
                    $(this).dialog("close");
                }
            }
        });
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