RescueTime comes with a Focus mode and a pre-seeded but configurable list of distracting websites: http://www.rescuetime.com/tour http://www.rescuetime.com/tour

RescueTime comes with a Focus mode and a pre-seeded but configurable list of distracting websites: http://www.rescuetime.com/tour http://www.rescuetime.com/tour You don't set hours of the day, but you specify how long you want to "Get Focused". And you can't close the utility via the GUI to keep you honest; it takes a manual SIGTERM to close while in Focus mode. I've found it very useful, though unfortunately browser support can be flaky. It seems like every major browser release breaks the website tracking and blocking functionality and it takes a few weeks to a few months for the RescueTime utility to catch up. If you don't like using uncommon OS/browser configurations, you'll probably have better luck, though.