We (the LW team) are definitely thinking about this issue, and I at least strongly prefer that people use the site in ways that reflect decisions which they would endorse in retrospect; ie, reading things that are valuable to them, at times and in quantities that make sense, and not as a way to avoid other things that might be more important. I'm particularly thinking about this in the context of the upcoming Recommendations system, which recommends older content; that has the potential to be more of an unlimited time sink, in contrast to reading recent posts (which are limited in number) or reading sequences (which is more like reading a book, which people have existing adaptations around).

A big problem with naively implemented noprocrast/leechblock-style features at the site level, is that they can backfire by shunting people into workarounds which make things worse. For example, if someone is procrastinating on their computer, noprocrast kicking in when they don't want to stop might make them start reading on their phone, creating bad habits around phone use. Cutting off access in the middle of reading a post (as opposed to between posts) is especially likely to do this; but enforcing a restriction only at load-time encourages opening lots of tabs, which is bad. And since people are likely to invest in setting personal rules around whatever mechanisms we build, there are switching cost if the first mechanism isn't quite right.

So: I definitely want us to have something in this space, and for it to be good. But it may take awhile.

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.