You don't have to wait exactly 3 or 5 years it is up to you when to take it. But 3 or 5 years is the minimum years required to take the test. You can wait however long you want to study. It is only questions about America.
Like what is the capital of the United States or who did we win our independence from or something like that. There might be a few that you don't know but it doesn't matter.
That's isn't all to it though it isn't that easy. You still have a little bit more to the test than just that. Another thing you have to do is read a sentence in English with no pauses or mistakes.
I hope now that this speech is over that you learned how to become an American citizen. Once you are done with all these steps, you will be an american citizen you will be able to join the military or stuff like that when you are done. This doesn't mean that you are no longer your original race because this didn't change anything about your old race.