The change of settings is applied to our filtering servers in a couple of minutes. Sometimes there will be no visible change in he filtering of prohibited websites. If after 5 minutes, don't see the changes you should make additional checks.
If you have recently visited the website that you want to block, then there can be outdated information in the cache of your browser, DNS cache of operating system, DNS cache of router and so on. Such outdated information can prevent your computer to block access to prohibited websites.
In most cases restart of the browser fixes the problem.
If after restarting the browser there are no changes, you should clear the DNS cache of your operating system.
You can do this on Windows OS with the command ipconfig /flushdns.
In uncommon cases, you need to clear the DNS cache of your router or proxy, if you have any.