"But you, Daniel, shut up the words, and seal the book, until the time of the end. Many shall run to and fro, and knowledge shall increase.” (Daniel 12:4)
The book pretended to have been written in the sixth century before Christ. However, most scholars admit that it was written during the Antiochus' persecution against the Jews about 164 BCE. So, the above verse was cleverly written to justify the appearance of a book which was unknown, although the author dishonestly lies by falsely foreseeing events of the Antiochus moment, as they were written in the sixth century.
Note also that the "time of the End" was the troubling time of the Antiochus persecution.