Here is a Screen Shot #1 comparison (click on image for bigger resolution):
And here is Screen Shot #2 comparison (click on image for bigger resolution):
It appears that since the Nexus 7 (left images) is a tablet and has more screen real estate then the smartphone Nexus 6 (right images) you get the alternative route time notifications as you are driving your selected route in Google Maps.
These notifications are actually a great feature, and I use it all the time for making real time route changes.
If anyone knows if there is actually a way to enable this on the Nexus 6 then please let me know.
NOTE: I did load up Waze on the Nexus 6 to see if that application had the route time notifications but from what I could tell it doesn't.