Publishers often allow their articles to be published in the repositories, but require a delay in publication, i.e. the article will be available a few months after the journal is published. This is the time the journal considers necessary to maintain its business model through subscriptions. These months of delay are what we call "embargo periods".
In the case of articles uploaded to Senia, you do not have to worry about embargo periods as the Library manages the opening date for articles in RiuNet.