Shikantaza, also known as "just sitting" meditation, is a form of meditation practiced in Soto Zen Buddhism. It is a simple yet profound practice that involves sitting in a relaxed and upright position, with a clear and open awareness of the present moment.

In terms of how long one should practice shikantaza meditation, there is no set time limit or prescribed duration. The length of the practice can vary depending on the individual's preference and ability. Some may choose to sit for just a few minutes, while others may sit for longer periods of time.

The key aspect of shikantaza meditation is not the length of time, but the quality of the practice. It is important to approach the practice with a sense of openness and curiosity, rather than striving for a specific outcome or goal. The goal of shikantaza is not to achieve a certain state of mind, but rather to simply be present and aware of whatever arises in the present moment.

With that being said, it is recommended to start with shorter periods of practice, gradually increasing the duration as one becomes more comfortable and familiar with the practice. This allows the mind and body to adjust and build endurance for longer periods of sitting.

It is also important to listen to one's own body and mind during the practice. If discomfort or restlessness arises, it is okay to adjust one's posture or take a short break. The key is to maintain a sense of ease and relaxation while sitting.

Ultimately, the length of shikantaza meditation practice is a personal choice and can vary from person to person. What is important is to approach the practice with a sense of openness, patience, and non-judgment. With regular practice, one may find that the length of time naturally increases as the mind becomes more settled and focused.

In conclusion, there is no specific time limit for shikantaza meditation. It is a practice that can be tailored to suit individual needs and abilities. The key is to approach the practice with a sense of openness and to listen to one's own body and mind. With dedication and patience, shikantaza meditation can bring about a sense of peace and clarity in one's daily life.