The pam module pam_time.so will allow a system administrator to define what time users can access certain services.

To deny ssh logins for the user rene during business hours add the following to /etc/security/time.conf

ssh;*;rene;!Wk0900-1730

Then add the following line to /etc/pam.d/ssh

account    required     pam_time.so

Check out the time.conf(5) and pam_tally(8) man pages for some more examples of time.conf entries.