According to Baidu’s official statement, Baidu has released an algorithm update in the end of May 2018 – Aurora Algorithm (Jiguang Algorithm, 极光算法), which is targeted to missing or abnormal release dates of posts.
To give audience a false impression that content of their websites is newly released, some site owners or SEOs choose to display posts on their websites randomly, without labeling release dates. This has become a widespread practice but is very harmful to user experience.
Therefore, Baidu has decided to take date formatting of landing pages as an important ranking factor.
Besides, Baidu has also provided regulations for submitting release date/time of content in case site owners have no idea how to mark them on their websites – Please use Google Translate if you need them in English.