Validating inline jquery Datepicker using jquery validation

I am trying to ensure that a date is selected using the built-in datepicker. The built-in datepicker provides a hidden input field, so this requires a tough requirement. To try to display the message, I moved my error messages using invalidHandler.

My code is:

<script type="text/javascript">
      jQuery('#date').datepicker({
        inline: true,   
        beforeShowDay: checkDayOfWeek,
        onSelect: function(dateText, inst) { $("#ship_date").val(dateText); }
      });
</script>

<div id="date" style="font-size: 75%;" class="required"></div>
<input type="hidden" name="ship_date" id="ship_date" class="required" />

Me moving error message:

jQuery("#custform").validate({
invalidHandler: function(e, validator) {
    var errors = validator.numberOfInvalids();
    if (errors) {
        var message = errors == 1
            ? 'You missed 1 field. It has been highlighted below'
            : 'You missed ' + errors + ' fields.  They have been highlighted     below';
        $("div.error span").html(message);
        $("div.error").show();
    } else {
        $("div.error").hide();
    }           
},
});

My goal: when someone submits a form without selecting a date, she is given a message to enter the date before submitting the form. If we can add a class to the div to select a date, all the better.

Thanks for reading