If you are always distracted from your work by wasting too much time online then StayFocusd is the Chrome Extension that you really need.

StayFocusd is a productivity extension for Google Chrome that helps you stay focused on work by restricting the amount of time you can spend browsing time-wasting websites. Once your allotted time for the day has been used up, the sites you have blocked will be inaccessible for the rest of the day.

StayFocusd is highly configurable. It allows you to block or allow entire sites, specific subdomains, specific paths, or even specific pages. Nice!