StayFocusd is one of the best Chrome extensions to block distracting websites while you work. It can be installed from here.
The options in StayFocusd are a bit different from other website-blocking extensions. However, once you learn about them, you wish other extensions had these features too.
Max time allowed: This is amount of time you are allowed to view the blocked websites in a day. By default, this is 10 minutes.
Active days: Choose the days of the week when you want StayFocusd to block websites.
Active hours: The hours of the day when StayFocusd should block websites.
Blocked sites: Here you can add the website domains which you would like to be blocked.
In addition to these settings, it is a good idea to enable the extension to work in Incognito Mode too.
Tried with: StayFocusd 1.4.7 and Chrome 31.0.1650.63