How long does it take to practice writing fine print with a brush?

There is no fixed number for this. Because of the time and seriousness of practice, whether there are good teachers and suitable teaching materials, how high the plans and standards are, and personal understanding of calligraphy are all factors to be considered. So how long it takes to practice varies from person to person, and there is no uniform standard. But personally, most people with average understanding need to practice for at least three months if they want to reach the junior high school level.