What I did in the end was to use window.setTimeout and window.clearTimeout:
var galleryToolTipTimer = null;
var previewElement = null;
$(document).ready(function () {
$("div#photos div a img").tooltip();
$("div#galleries ul li:not(.active) a")
.tooltip({ items: "a", content: 'Loading preview...', disabled: true, open: function (event, ui) { previewElement.appendTo(ui.tooltip.empty()); } })
.mouseover(function (e) {
if (galleryToolTipTimer != null) { window.clearTimeout(galleryToolTipTimer); }
var aLinkObject = $(this);
galleryToolTipTimer = window.setTimeout(function () { previewGallery(aLinkObject); }, 500);
}).mouseleave(function (e) {
window.clearTimeout(galleryToolTipTimer);
$(this).tooltip("option", { disabled: true });
});
});
function previewGallery(aLinkElement) {
previewElement = $("<div/>").load(aLinkElement.closest("div").data("galleryPreview") + "/" + aLinkElement.data("path") + " #preview", function () {
aLinkElement.tooltip("open");
});
}
Works at least the way I want.
To see it in action, simply navigate to http://fotos.amon.cc/ and hover over one of the gallery links on the left for a preview: