Restricting access to the system (OS - Windows) of a user on a time interval defined by the admin (computer administrator ), is possible using Command Prompt (Start - Run - cmd) and following a command line that will include User name to be restricted si time restrictions.
A few examples:
1. net user Ana / time: MW, 09: 00-17: 00
2. net user Cristina / time: MF, 5 am-3pm
3. net user Ionut /time:M,4am-5pm;T,1pm-3pm;W-F,8:00-17:00
4. net user Ciprian / Time: all (In this way the user can log in at any time)