I'm a fan of the Pomodoro method when working. I find chunking time in 25 minute increments to be a reasonable cadence for work - systems design & product development/engineering.
I wanted to add a Pomodoro timer to my app, Nag, and decided to use moment.js for some of the time manipulations.
Here's the result:
A pomodoro timer, implemented in the browser with Bootstrap and moment.js.