This is the Latinate plural for administrative, found also in Spanish and Romanian, and is preferred in formal use, but the earlier more humorous and pejorative blend administrivia is much more commonly used. Even more common are more informal terms such as paperwork.
As a Latin plural, in formal usage used as a plural, as if it were “administrative tasks” – “administrativia take hours each day”. More common is to use it as a singular collective noun – “administrativia takes hours each day”. Compare to usage of other Latin plurals such as data.