After obtaining the DNA and Chakra necessary to gain the Rinnegan, you must wait precisely five years IRP to begin seeing the effects. These are your odds of getting a certain stage of the Rinnegan. There is no way to speed up the process. In order to obtain all four eyes, you will need to wait for five years after gaining each one separately. As soon as you gain one eye, new tissues grow in its place, making it difficult to tell where one tissue ends and another begins. This means that you could have already obtained a second or third eye even though you don't know it yet! It is important to note that while you are waiting for these eyes to develop, there is nothing stopping you from using themies. If you go more than five years without viewing an image in a mirror, you will eventually lose track of what you look like and become disoriented when trying to find your way out of a room. If this happens to you, take out your smartphone and scan something. You will then be able to see in your reflection again. However, if you leave the world of the living for too long of a period of time, you will die. So be sure to keep yourself occupied by playing games, reading books, etc. during your wait.