Leechblock NG [1] allows you to block sites on a schedule or add time limits.

[1] https://www.proginosko.com/leechblock/

This is somewhat tangential, but related: if you are savvy enough to setup some self-hosted apps, I have used FreshRSS (along with some related extensions/plugins) to great effect in an effort to remove the direct influence of algorithms and endless scrolling.

With some tweaks, I can even use it to maintain subscriptions to YouTube channels and social media feeds. It’s maybe a subtle distinction, but I feel like having a very prosaic, chronological list of posts/articles/videos promotes healthier habits for consuming them.

Create a separate, non-admin user account that is controled by any parental control apps, parental proxy filters etc. and use that one for work or during leisure time. You can then time-lock your admin- or parental control password using an online time lock service such as lockmeout.online or other solutions.

if you're on a mac or linux you can always edit /etc/hosts to redirect traffic to localhost, effectively killing the site on your local machine

https://freedom.to/ Works everywhere for me.