There is no logout function.
In 5.3 you can restrict users login to specific days and times, say from 8:00 am to 5:00 pm. I am not sure what happens to any users still logged in at 5:00 pm, but I somehow doubt if they will be forcefully logged out.
In Accpac you can click on Help, Lanpak Users and get a list of active users, and then ask them to logout.
Backups are normally run late evening or early morning, so there should not be any active users. Any user still active in Accpac has simple forgotten to logout, and normally a warning letter will resolve that problem.