ppp question...

[Xpression]

        Hi list...I'm revised the ppp man pages and not getting me any
clues, I'm running TACACS+ on a FreeBSD server and I want to disconnect all
user at any time (12:00 pm). I mean, user call to a number XX-XXXX and the
call are received by 3 modems connected to a router (Cisco 2500), the server
authenticates users by TACACS+ service...but I can't disconnect users
without login on the NAS...any clues ???