Hi, I have successfully solved several parts of your project before. There are also Windows-based open source projects (developer tools) to take inspiration from. The app should have a back-end built as a Windows service, so it can recover on reboot or a manual attempt to kill the process. Time duration can also be made robust so it persists between reboots. Black/white list is not a problem, it can block access to an entire domain or just selected pages. The request for blocking access through all networks rather than selectively makes the project actually less difficult.
The appearance can be entirely custom or system-based.
I am currently in the process of building my new portfolio website, so I'll update this proposal with a link by tomorrow, or you can let me know and I'll send you screenshots etc.
Also let me know if you need a list of technologies I plan to use or any other detail.