It is a special state of regulating body and mind, and it does not enter the grain. The length of time depends on everyone's specific situation, especially closely related to a person's physical health, psychological quality and practice foundation. A long time is good for health and practice, but the longer the time, the better. Guo's Daoism and Daoism are based on seven days, because cells in our body have a seven-day metabolic cycle.