Your game will pop up a notification if you are approaching your 35 hour game time limit. If you enter a cool-down period, take a break and/or catch some sleep. Note that when your cool-down is lifted it's not advisable to start playing long hours again as you may face another cool-down period (some of your previous hours of play prior to cool-down will be included in the new counter/timer).
For a better explanation of what is meant by this, please check out this tutorial video: http://bit.ly/PFepAk
To conclude, if you were logged in for more than 35 hours in the 48 hour period, it is recommended waiting a couple of extra hours after the cool-down expiration to ensure that your game isn't placed on an additional 12-hour cool-down. Also please make sure your browser doesn't have any plugins or addons that prevent your account from going offline as this contributes greatly to your cool-down countdown and is a bannable offense.
Keywords: locked, 12-hour, cool-down, cooldown,