allow/deny user power of the os

[Pol Hallen <debenvaio@fuckaround.org>]

hi folks :)

How is the best way to deny and allow by time and date of user/s 
poweroff/reboot system?

This client runs from 08am to 8pm. I have to deny all users reboot or poweroff 
within time, but user/s can reboot or poweroff this system from 8.01pm to 
7.59am.

Thanks!
 
Pol