Hacker News has a feature called "noprocrast". Here's how they explain it in the FAQ:
In my profile, what is noprocrast?
It's a way to help you prevent yourself from spending too much time on HN. If you turn it on you'll only be allowed to visit the site for maxvisit minutes at a time, with gaps of minaway minutes in between. The defaults are 20 and 180, which would let you view the site for 20 minutes at a time, and then not allow you back in for 3 hours.
If you try to use HN when you precommitted to not using it, you'll get the following message from them:
Get back to work!
Sorry, you can't see this page. Based on the anti-procrastination parameters you set in your profile, you'll be able to use the site again in 43 minutes.
I was thinking that something like this would be awesome for LessWrong. Personally, I have a rather large problem browsing the web - which includes browsing LessWrong - when I should be doing other things. After reading Digital Minimalism, I get the impression that such struggles are moreso the norm than the exception.
You can use leechblock to add time restrictions for any site.
It also has the option to add loading delays to sites, which I find useful for sites which I can't afford to block outright.
Leechblock is excellent. I presently use it to block facebook (except for events and permalinks to specific posts) all the time except for 10min between 10pm and midnight; I have a list of webcomics that I can only view on saturdays; there is a web-based game that I can play once every saturday (whereafter the expired time prevents me from playing a second game), etc.