After becoming a RN it takes around 4 to 6 more years to become a nurse practitioner.
To become a nurse practitioner you need to complete an Associate's degree program to get your Associates Degree which takes two years and then you also need to complete a bachelor's degree program to get your bachelor's degree which takes 4 years.
So expect it to take at least 6 years to become a nurse practitioner unless you already have those degrees.