Google Maps has dropped its in-traffic travel estimation features, which was estimating how much time it would take to drive somewhere with traffic, either live traffic or predictive traffic based on day/time.
Google had launched traffic estimates back in 2007
A Googler in a Google Maps Help forum thread, explaining that they have removed the feature because it wasn't accurate enough. Per Daniel's explaination:
We have decided that our information systems behind this feature were not as good as they could be. Therefore, we have taken this offline and are currently working to come up with a better, more accurate solution. We are always working to bring you the best Google Maps experience with updates like these!
However, the dynamic travel-time prediction feature still exists on Google Maps for Mobile on iPhone and Android phones. For example, Google Navigation for Android will dynamically estimate how far you are from your intended destination. However that system uses GPS to determine distance and travel time.