Yammer Time has been discontinued.
Yammer is a service designed to help co-workers keep each other up-to-date on their work progress by answering the question "What are you working on?"
Yammer Time is a Firefox extension that reminds you to use Yammer. By default, every 4 hours between 9AM and 5PM on weekdays, it will pop up this obtrusive prompt:
Just tell it what you're working on (you are working, aren't you?), and it will go away for the next 4 hours. You can change how often it asks (and on what days) in the Preferences dialog. You can also manually update Yammer by clicking on the Yammer Time toolbar button: