PRISM Namespace is consolidate all rights related elements within a single namespace. AFAIK oob does not use it & may be as part of meta data extraction it might exist.
Offtime just adds attribute as properties to the content & when you activate content will be available in publish. When Off time matches or greater than current time , AEM OSGI Services consider that content as dead and if you try to access using HTTP, AEM would return 404 error but content will still leave in publish instance. if you don;t want content to stay then need to deactivate.