Wifi access settings for device group

I want to limit the total numbers of hours my child can spend on wifi across all his devices.
Example: he has three devices and I want the total time any/all of them can spend on wifi to be three hours. This means he can spend three hours on one device OR one hour on each device. I want that to be his choice. The router/app should enforce the total time limit though.
* I already limit the beginning and ending time he can use the wifi. This is not what I need help controlling.
* I want to be able to add specific devices to the controlled group (his devices may change over time)
* I want to exclude other devices from the group. In other words, some devices on our network should not be limited.
* The controlled group is multiple-platform. Specifically, the group should include an Xbox, playstation, TV, ipad, apple laptop and Nintendo switch.
Because of the multiple platforms, I anticipate a router-level solution works best.
* We currently have Google nest wifi.

Project will be complete when the above description is implemented.
You will not have access to our network. However, you can tell us what settings to change or what new router / application / program to buy.