Pu-erh is not like ordinary loose tea so it's quite safe to do that. Without stirring or pressing, you don't get too much of the flavor into the water and it's much more coarse. You'll find a lot of the green teas also don't over-flavor the water because of this.
Depends. I can leave my Pu-Erh in overnight, and the flavour is still fine. (But Pu-Erh is well known for that.)