DATEDIFF возвращает NULL в начале триггера INSERT

Вы можете использовать submitHandler из формы JQuery validate plugin

<script type="text/javascript" src="resources/jquery.min.js" ></script> 
<script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.11.1/jquery.validate.min.js"></script>
<script type='text/javascript'>
$(document).ready(function() {
    $(".form").validate({
        rules: {
            userName: {
                required: true
            },
            password: {
                required: true
            }
        },
        messages: {
            userName: {
                required: "specify userName"
            },
            password: {
                required: "specify password"
            }
        },
        errorClass: "help-inline text-danger",
        errorElement: "span",
        highlight: function(element, errorClass, validClass) {
            $(element).parents('.form-group').addClass('has-error');
        },
        unhighlight: function(element, errorClass, validClass) {
            $(element).parents('.form-group').removeClass('has-error');
            $(element).parents('.form-group').addClass('has-success');
        },
        submitHandler: function(form,e) {
            e.preventDefault();
            console.log('Form submitted');
            $.ajax({
                type: 'POST',
                url: 'authenticate.jsp',
                dataType: "html",
                data: $('form').serialize(),
                success: function(result) {
                    window.location.href = "dashboard.jsp";
                },
                error : function(error) {

                }
            });
            return false;
        }
    });

});  
</script>