WebTime. Keep tabs on your tabs.
WebTime is a dead-simple Chrome extension that keeps track of how much time you spend on certain sites each day.
You configure a list of sites on which you want to track time, and a daily time limit. WebTime gives you a colored icon in the toolbar to help you keep track of your daily time on those sites.
The toolbar icon changes slowly from green --> yellow --> orange --> red. When you're on a listed site, it shows you your total minutes today on your site list. If you've gone over your alotment, it adds '!'.
I find it useful to know how much time I'm spending 'unproductively'. I set my list to be domains that I go when I'm bored, e.g. 'cnn.com', 'techcrunch.com', etc.
PRIVACY: WebTime runs only on your computer and never sends any data anywhere. WebTime only knows what URL you have open.
WebTime is free and open source: https://github.com/jdurack/WebTime