They are dated, in each user's settings you can see them. But the dates are not publicly shown as these dates can be used to prove that you were the first to publish it.
If another website copies your hub, they can simply put the date before your publication date and you have no proof that you were the original author. But if you have the real date the content appeared on the web then you can prove to search engines that you were the first to publish it. Search engines also know that date because they crawl the web daily for new content.