NAS features info

Hi, Is there a document that I consult so I know what to look for if I want more than just authentication with radius ? I would like to buy a wireless accesspoint where I can "time" user-access, meaning my users are restricted in time when they can use the wireless accesspoint, and force them off-line when their time-window closes. Because I don't know how this is managed, I can't decide which accesspoint will do what I would like to do. All such stuff, is that read/managed via snmp ? Regards, Koenraad Lelong