Howard Hill shot many, maybe hundreds, of arrows every day. When he wasn't actually shooting arrows, he would often pretend to shoot arrows and visualize the path of the arrow through the air to the target.
About 8 months ago, I started shooting just about every morning with some friends. We vary between stump shooting at unknown distances and target shooting at known distances. I would guess I shoot about 50 arrows every day. My shooting has improved a lot since I started shooting with them. Before, I would probably average 5-10 arrows a day, which I don't really believe is enough to hone your form.
Interestingly, when you shoot at the same archery range every morning, after a while there isn't any such thing as an "unknown distance" anymore, even though it is a rather large range covering many acres. Even if you throw a tennis ball out in the middle of a field, you have walked across that field enough times, and shot at enough other things in that field, that you have a good idea of how far away the tennis ball is. This was brought to my attention when I shot at another archery range recently, unmarked distances, and didn't do anywhere near as good as I did at my home range, since I wasn't familiar with the territory.