Google Wifi has a pretty good system built in. We set up a ‘group’ for each kid then turned WiFi off on a schedule. We could also pause Wifi for one or all 3 kids whenever we needed/wanted to by tapping on the app or by telling our Google Hub to pause the Wifi. Not impossible to bypass (hot spots on phones for example) but worked pretty well until they aged to control their own usage. You can also just go take a power cord or other unique component away for a while.