Delay in NextDNS taking effect

NextDNS is set up to restrict devices from certain websites. 

Apparently, it takes 15 minutes for Mac device to get blocked on restricted sites from time of starting up computer.

When user shuts down computer and than starts it up again, restrictions again do not take effect for 15 minutes.

Is there something that can be done to prevent Mac user from circumventing restrictions by repeatedly starting and shutting down PC?