Chrome Nanny

A powerful Chrome extension for blocking distracting websites, either all the time or on a schedule.

Multiple block sets – Have different sets for different times or days of the week.
Flexible scheduling – Choose the time to block websites based on the day and time. Multiple times can be scheduled to allow for unblocking during certain times (ideal for lunch breaks).
Protected settings – Settings page can optionally be protected to prevent the temptation to unblock sites.

con Time consuming to add lots of urls
Have to add each url one at a time using a form. Flexible, but takes a while to add a lot of websites.