npm install clit
or [sudo] npm install clit -g if you want to use clit as a standalone executable.
If you installed clit globally, just run clit to start the timer.
If you did not, go to the folder that contains the repo, and run node clit.
Enter Ctrl+Z to pause the timer, and to unpause it if it's already paused.
Enter Ctrl+C to stop and quit the timer.
The complete source code is contained in clit.js. It is about 70 lines long.
clit is written by Federico Pereiro (fpereiro@gmail.com) and released into the public domain.