I have had mine pierced for over 20 years, long before I became a piercer.
8-10 weeks is a good time frame, though most of them heal more quickly than that. It is a good idea to not change the jewelry until then, even if it seems to be healed.
If you are going to use nose bones, the ones with the ball on the end, it is especially important that it be completely healed. If it is not, the hole may heal to the size of the stem. Then you will have 2 choices, either rip the piercing open pulling it through to change it, then have to heal it all over again, or have it cut out, and take the chance of the wire cutters cutting you, the cut part flying into your eye, or if you cut it from the inside, it can actually go up your nose. I am not trying to scare you, I just don't want this to happen to you. I know the nose bones are often cuter and fancier that many of the rings or screws, but I really do not care for them. They come out more easily than other kinds of jewelry. I have always had good luck with screws.
vespacat, I was not piercing quite that long ago, but I was observing for the time I knew was coming when I would learn. Needles have always been best, with small rings. I know a lot of people have goe to screws, but they don't heal as well, come out more easily, and are much harder to care for.
I would NEVER, NEVER, NEVER pierce anything with a gun. They are hotbeds of infection and are almost never accurate.