In the past, occasionally when working late on a project I would turn off my wifi to avoid visiting time-wasting websites (like, oh, I don't know....maybe this forum?).

I just found a new extension for google chrome that limits the time you spend on certain websites. It has a lot of customizable options, including the option to make you take an annoying typing test before you can change the settings. I tried it and it takes a while to pass this test.

https://chrome.google.com/extensions/detail/laankejkbhbdhmipfmgcngdelahlfoji