You might try Security/3000 by VESoft. It allows you to restrict user
logons by time-of-day, day-of-week, device number, and any other number
of attributes. You can also put extra passwords to modems, enforce
password expiration, keep a list of forbidden choices for new passwords
(such as easy to guess or a common word) or require that they match a
pattern (such as 3 alpha followed by 4 numbers), and so on. Very
powerful.