I agree with David, make sure you log out or at least use the Preview mode.
So you're aware, if you have basic publishing workflow enabled what will happen is if you have a document type already published and make a change to it, then add a publish from and to date, the already published content will remain visible until the publish from date is reached and that new content is published.
Then assuming there isn't another version of the content, when the publish to date is met, the page will be unavailable or return a 404 when someone accesses it.