Talk to any master practitioners of tai chi and they will tell you that zhong ding and dantian are the two most important concepts in tai chi and Chinese internal martial arts. They are also the most basic. They are the two things you will work on for as long as you do tai chi. Hopefully, that will be a lifetime. It doesn’t take long to understand the concepts, just a lifetime to develop them and enjoy the benefits almost immediately.
On Healing and the Mind, Bill Moyer’s show, Volume 1, The Mystery of Chi, the teacher of my lineage (Grandmaster Ma Yueh Liang) told him that it took him 10 years to understand what Chi is and the rest of his life to learn what to do with it. He was in his eighties at the time. This is how it is with everyone who delves into the vast universe of the supreme ultimate art of movement.