With the guidance of teachers, you can take fewer detours, and your illness will be more serious if you practice wrong. Moreover, how long you practice every day is not a fixed number. For example, after the operation, the body is weak, and it is no problem to practice for a period of time every day, with the goal of recovery; For example, if you are in good health, you can practice for a while. Depending on your personal situation, an hour or so is enough.
Then talk about what kind of Tai Ji Chuan to practice. At present, there are six kinds recognized by Tai Ji Chuan countries: Chen, Yang, Wu, Wu, He, and their development order is roughly the same. Chen more worked hard, because it was the earliest Tai Ji Chuan, so it was similar to Waijiaquan. Yang developed from Chen, with less strength, and paid more attention to the application of internal strength than chen more. Then there is Wu, which developed from Yang and has been teaching princes and ministers in the imperial court, so it is softer, pays more attention to health preservation, and is more suitable for older people where there is no strength; I don't know much about Takeshi, Sun Shi and Choi-hi, so I won't talk about it, but Choi-hi is recently recognized as a relatively new Tai Ji Chuan.
I suggest that your parents don't practice Chen, because when they are old, they don't need to learn how to attack with strength, so they are easy to get hurt, so most of them learn Chen from young people, such as Jet Li and the first one. I think it's best to practice Yang style or Wu style. Yang style has little strength and can be practiced without strength at all, mainly focusing on health preservation; The same is true of Wu, who originally gave health care to princes and ministers, so it may be more appropriate. However, no matter whether you practice Yang or Wu, you should practice traditional boxing, not those game routines, because the game routines need time and movements to look good, meet the standards and facilitate the referee, but there are still shortcomings in transfer, ventilation and health care.
Finally, find a good teacher and wish your parents good health.