This relatively short python script is deceivingly useful. It helps you to pace your workflow, and be more aware of your free time.
To install it, simply add the following file to your /home/USER/bin directory, and give it execute permission.
To customize it, open the file with your favorite text editor and change the times at the top. You may also wish to change the window properties found at the bottom of the file. You can repurpose it to show how much time you have left at work by also changing the notification messages in the middle of the file from "Go to sleep" to "Hurray! Work's over!"
To run the file in gnome, press ALT + F2, then type "timeleft.py". You can also run it by double clicking the file, or making a shortcut that runs the command "timeleft.py"
The script is licensed under the CC-GNU GPL version 2.0 or later.