Nanny works just like LeechBlock. Go to Settings > Extensions > Nanny > Options and add the websites and times of the day when they should be blocked. If you visit those websites during those times, Nanny throws up a message not allowing access.
Nanny is simple and does what is promises. The only problem I have with Nanny is that its settings do not seem to be synced between the many computers I use Chrome on. So, I end up having to set the block settings manually on every computer.
Tried with: Nanny for Google Chrome 0.990 and Google Chrome 25.0.1364.152