The length of time for practicing Zazen, or seated meditation, can vary depending on personal preference and experience level. However, it is generally recommended to start with shorter sessions and gradually increase the duration as you become more comfortable with the practice.

For beginners, it is suggested to start with 5-10 minutes of Zazen and gradually increase by 5 minutes each week until you reach a comfortable duration. This allows your body and mind to adjust to the practice without feeling overwhelmed.

As you become more experienced, you may choose to sit for longer periods of time, anywhere from 20-45 minutes. Some practitioners even sit for an hour or more, but this is not necessary and should only be done if it feels comfortable for you.

It is important to listen to your body and not push yourself beyond your limits. If you feel any discomfort or pain, it is okay to adjust your posture or take a break. The key is to find a balance between challenging yourself and being gentle with your body.

Additionally, the frequency of your Zazen practice is more important than the duration. It is better to have shorter, consistent sessions rather than longer, sporadic ones. Aim for practicing Zazen at least once a day, but if that is not possible, try to do it at least a few times a week.

Remember, the purpose of Zazen is not to achieve a certain length of time, but rather to cultivate a clear and focused mind. So, whether you sit for 5 minutes or 45 minutes, the most important thing is to approach the practice with a calm and open mind.

In summary, there is no set time for how long one should practice Zazen. It is a personal journey and the duration should be adjusted according to your own needs and abilities. Start with shorter sessions and gradually increase as you become more comfortable. And most importantly, listen to your body and approach the practice with a gentle and mindful attitude.