The GSDs I grew up with would do it pretty immediately, but I had to occasionally praise them when they did it so they wouldn't lose the habit. They're pretty damn smart and will figure out some pretty complex behaviors just from positive reinforcement. I once taught a GSD in one session to sit patiently 10 feet away from the vehicle gate at my childhood home when I arrived home by stopping the truck every time started walking forward. By the 3rd or 4th time of my inching forward he had figured out that the only way to get me to pull in and get out of the truck was to sit patiently and I never had to train him on it again.