How this is possible in your opinion? Only whit a squid? It is no possibile to customize / make a script inside of Mikrotik proxy that interrupt user navigation?
I actually have something like you want, just preparing it for the market. But a proxy is MUST. Contact me with private message, if interested in details.
In production already. However, as it seems to be “A Hot Topic”, only contact via email. Look at my profile.
And, it is a commercial solution, not bound to MT. Actually being implemented in USA on Open-Mesh equipment, too.