If you are a beginner, it may take a lot of time and energy to master the eight-character prediction by self-study. You need to read related books, study related courses, watch teaching videos, practice horoscope prediction and so on. Usually, it takes several months to a year to learn eight characters.
If you are an intermediate or advanced eight-character learner, it may take longer to master eight-character prediction. In addition, you need to have a certain talent and understanding, as well as a lot of practice and experience accumulation. Usually, it takes one to several years to learn eight characters.
In short, the time needed to learn the eight characters depends on your learning style, learning time, your talent and hard work, so you can't give an exact time. I suggest you keep patience and perseverance in the process of learning eight-character prediction, keep learning and practicing, and constantly improve your level.