Best approach on (time scheduled) block internet access for specific hosts but allow (or block) others on demand

Hello,

We've been asked to block internet access during a specific time for some devices, and I guess we can do it via MAC or IP hosts. However, this first question came up:

What if the "blocked" clients use other device to access internet? How can we give access (or block access) to a specific device that is not part of the known network?

Best regards

Kostas