I do roughly 90% of my driving on German Autobahns.
Navigator's route settings in Route Info are set to "Schnellste/fastest".
Occasionally, I notice this phenomenon:
Navigator recalculates my route and asks me to leave the Autobahn. I see the ETA. stay on the Autobahn, and seconds later, after the route has been re- recalculated, I see an earlier ETA (usually several minutes) than with the diversion.