If you're using a home router with a broadband connection, you should be able to restrict internet access hours via the router's configuration setup pages.
For instance, on a Linksys WRT54G v5 home router, internet access can be allowed or denied based upon "day of week" and/or "time of day". From the home configuration page of this router, select the "Access Restrictions" tab which displays "Internet Access" configuration page.
