I mostly automate it: Their phone won't function after bedtime (except for emergency use like calling 911), their devices cannot connect to the network until morning, and physical access is restricted unless it's the appropriate time.
The wifi itself isn't shutting off, it's just blocking certain computers and if they are smart enough to manually change their MAC address, you would need to revert to controls local to their machines, but on my home router, it's a standard feature: I just logged into the local DNS web app for managing the router and added the MAC addresses.
For local device management, it varies depending on the device but broadly speaking there are usually built in parental controls for most Microsoft/Android/Apple devices: It's just a matter of configuring them.
That said, a low-tech solution to this if you didn't care if your network went down would be to either manually turn it off or attach it to a timer to automatically shut it off. I don't go this route because I still want Internet after bedtime and sometimes do overnight downloads/updates.