Google Now is an app for providing personalized services based on user interactions. One of the services it provides is the estimated time of commute via Google Maps. Google now provides intelligent notifications on mobile about the commuting time from Home to Work and vice versa.
In order to ensure a user is retained with Google Now on a daily basis, rather than letting user manually clicking and checking for commuting time, they provide the approximate time already as a mobile notification based on time of day, thus doing two things at once, motivating users to go inside and know the directions and that too in a single tap.