Hi Adam.
Can you provide more description of the issue?
Are you referring to the external calls or the users who are on the same Phonesystem can not call internally between them too?
Maybe you can provide more information here.
What Phonesystem version is used?
Are you using Deskphones if so are they local to the PBX or remote or its 3CX applications if so, are they Weblcients or Mobile applications?
Instead of switching the users to Away, set the office hours on the department and set the out of office call handling there. "When office is closed route to..." Then the users remain Available.