This relates to the date the news item was created. Let’s say your office holds an annual event, and you posted a news item about it last year. As the event approaches again this year, should you create a new news post? Yes.
If you edited the post from the previous year with updated information, the date of creation will remain that of a year ago, so it will not be included in 鶹Ƶ Daily, nor will it move to the top of your site's news feed. Re-editing old news posts is something you want to avoid for other reasons as well, including that subscribers to your news feed will not receive notification of a new post.