Or you can use the focus event on your dateSelect object and position api together. You can swap top and bottom and left for right or center (or really anything you want from the position api). This way you don't need an interval or any insanely complex solution and you can configure the layout to suit your needs depending on where the input is.
dateSelect.focus(function () {
$("#ui-datepicker-div").position({
my: "left top",
at: "left bottom",
of: $(this)
});
});