Maybe a lightweight proxy server (running a r-Pi? or another headless server) on your network and routing traffic through it? I offer this as an extension to my post many comments down, which basically covers my belief that you must first filter/proxy the mind. Not trying to control how to hand everything the world has available but instead only allowing yourself to focus on what you need available and saying no to the rest.

Anyways, it's bit of a time consumer setting up said software initially but you benefit from a lot of angles once done. (Network security, content management, less likely to back track on systems that take more work to implement, as well as having a sophisticated and global system across all devices routed through the proxy server.) I believe some software packages even allow for the management of access times as well as content type. White list only a couple sites/ url's / IP's you use and white list them for only the time you need to be able to use them. Have someone else change the computer password on the server that you trust and boom. Just don't get distracted trying to circumvent security now...ha ha

Just a casual suggestion based upon experience as a school system administrator. Normally though if I am having a problem that starts in the mind, I develop a solution that either starts there or starts at whatever triggers it in my mind. Just a thought. Hack yourself you know?