"Now, you can avoid the wait and see the busiest times of the week at millions of places and businesses around the world directly from Google Search. For example, just search for "Blue Bottle Williamsburg", tap on the title and see how busy it gets throughout the day," informs Google.
For now, it seems that this feature is only available in the mobile interface. Google says that the data is based on historical visits, so I assume it uses Location History and other location services for mobile devices. Google Maps has a similar feature that shows typical traffic.