mine don't need 4 hours a day either, but Masi IS an energizer bunny
I do different things depending on the day, she's always out first thing in the morning, while I'm doing outside stuff, on days that I don't work, she usually goes with me when I run errands, we may take a hike, a walk, frisbee throwing broken up along the day. Night, she's out with me/husband for awhile,
I don't think I can really calculate 'how much' exercise she gets a day, it's always different, but she does get to do "something" each day.
If I had to leave her all day, with nothing to do, oh yeah, by the end of the day she is wound up and ready..
Since she's matured, she has a good off switch, and like most of the other gsd's I've had, she's ready to go when I'm ready to go, would go all day if that were the case, or hang out all day as well...