Maybe look at using Net Nanny parental control software. Google it.
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Every headset has a MAC address. Most WiFi routers have parental controls. Program the router to only allow Internet connectivity during certain hours, from the headset's MAC address. Also, the description of every app in the Oculus Store tells you if Internet Connectivity is required. There are a smattering of games that actually DO NOT require Internet connectivity; like Eleven Table Tennis VR.