StayFocusd is a productivity extension for Google Chrome that lets you restrict the amount of time you can spend per day on time-wasting websites. For instance, you could specify a 10 minute limit for Facebook and it will auto-block the website in your browser after that limit has passed.
You have the option to block entire domains or a subdomain – for instance, you may choose to block www.facebook.com but not developers.facebook.com. You can turn off StayFocusd on weekends, or allow it to only run on certain days of the week.
StayFocusd offers a Nuclear Option as well allowing you to block access to all website except for the work-related ones that you have put in the Allowed Sites. You can launch the Nuclear option on demand or at a scheduled time. It can block entire sites, or just selected elements like media files or images.