InternetOff is a program that comes in handy if you wish to immediately disable your Internet connection and work offline. The application is very intuitive, has easy-to-configure settings, and doesn't slow down the performance of your system while running in the background.
This network tool lives in your system tray from where you can disable and enable Internet access and configure the app's advanced settings according to your needs. In my testing, it immediately applied the necessary changes.
Furthermore, you can decide when and how long you need the application to disable your Internet connection. The correspondent option can be found in the Settings panel of the utility.
The one thing I'd add to this program would be an option to save multiple schedule profiles. For example, I would have an InternetOff schedule for my work time and another for when my kids are using the computer for homeworks.
Other than that, there's nothing I would change about this program. It's easy-to-use, efficient, works fast, and is free.