Windows 7 Parent Controls gives option for setting time limits to a user account. This can be accessed using Control Panel -> Under User Accounts and Family Safety -> Set up parental controls for any user
On selecting the required user account, the following User Controls window would be displayed
Make sure to select the radio button with label as On, enforce current settings and click on the Time limits link listed under Windows Settings. This displays the Time Restrictions window as shown below.
Select the required day and the time for which restricted access has to be given. The blocked time period would be highlighted in blue color.
After making this changes for the User account and if the Use tries logon to Windows 7 System, then an error message would be shown and user will not be allowed to logon to the system.