Edit in JSFiddle

$('form').validate({
    rules: {
        name: { required: true },
        email: { required: true, email: true },
        pw: { required: true }
    },
    
    submitHandler: function (form)
    {
        $('form input:submit').attr('disabled', 'disabled');
       
        interval = window.setInterval(function ()
        {
            var text = $('form input:submit').val();
            if (text.length < 5)
            {
                $('form input:submit').val(text + '.');
               
            } else
            {
                $('form input:submit').val('送出');
            }
        }, 200);
        //為了示範方便所以先註解掉真正送出的呼叫
        //form.submit();

    }
});

<form action="/test" method="post">
      <p><label for="name">姓名：</label> <input id="name" name="name" type="text" value="" /></p>
      <p><label for="email">電郵：</label> <input id="email" name="email" type="text" value="" /></p>
      <p><label for="pw">密碼：</label> <input id="pw" name="pw" type="text" value="" /></p>
      <input type="submit" value="送出" />
</form>