Do you want to know if you wrote a really good book and self-published it on Amazon, how long will it take for the book to become a top seller if you are unknown and did little to no advertising?

OK, you don’t want to hear this. No first-time author wants to hear this, and a self-published author never wants to confront these realities.
To begin with “a really good book” is a totally subjective measure. Because you think you’ve written a really good book doesn’t mean that I will like it, or participants on GoodReads will like it, or your intended audience will like it. Hell, I’ve read some critically acclaimed works that I’ve hated.
Next is the core problem.
Let’s say that in fact, you’ve written the definitive Great American Novel. No one reading it would doubt the merits of your book. You self-publish. It’s on Amazon. You do nothing to support it, either because you don’t have the money to buy ads and pay a marketing professional, or because of some other reason.
Your book will not sell itself. People will not suddenly become aware of it. There is no magic and no secret sauce.
A traditional publisher employs people who send out review copies, get the store and online placements, buy ads, and work with the author on interviews, signings, and appearances. Doing all of these things on your own is pretty much a full-time job. Paying independent consultants gets expensive.
If you self-publish, even if it’s the best book ever, it is very unlikely that it will become a top seller. Even if you self promotes, and certainly if you do little or nothing. Even if you have a friend who is a famous and bestselling author who champions your work.
Now that I’ve probably put a damper on your day, I’ll say this.
If you want to self-publish, go for it. Write the best book that you can. Try to get your friends to read it. Use it as a platform to get more attention down the road. Consider it a learning experience. And most importantly, consider your own expectations and priorities.
Do you want to make money from your work? Develop a literary reputation? Get feedback? Something else? Answer these questions for yourself, and you’ll have some idea of what, besides having the book on Amazon, you need or want to do.