Abstract: A cover is releasably secured over an opening by an apparatus or a fastener system and may be used in a book-clock system having a clock movement housed within a space hollowed through the book's pages. A clock shaft protruding from the movement passes through an opening in a fastening element and then through a hole in the book's front cover. The clock shaft supports and moves the clock hands on the front. The fastening element may be a flexible strip. It may be positioned in a U-shape about the clock movement so at least a ferromagnetic part of the fastening element is adjacent to portion of the clock movement facing the back cover. A magnet is positioned on the back cover so when closed, the magnet meets the ferromagnetic part of the fastening element. A magnetic force is exerted and releasably holds the back cover of the book closed.