Zazen, or seated meditation, is the core practice of Zen Buddhism. It involves sitting in a specific posture and focusing on the breath to quiet the mind and cultivate inner peace and insight. While there are no hard and fast rules about when or where to practice Zazen, there are some general guidelines that can help practitioners establish a regular and effective practice.

Traditionally, Zazen is practiced in a quiet and dedicated space, often referred to as a "Zendo." This can be a room in one's home or a designated meditation hall in a Zen center or temple. The space should be clean, uncluttered, and free from distractions. Some practitioners also like to create a simple altar with a candle, incense, and a small statue or image of the Buddha to help create a sacred atmosphere.

In terms of timing, Zazen can be practiced at any time of day, but traditionally it is recommended to practice in the early morning or evening, before or after daily activities. The stillness and quiet of these times can help to create a conducive environment for meditation. However, if these times are not feasible, one can practice at any time that works best for their schedule.

The length of a Zazen session can vary, but it is generally recommended to start with shorter sessions, such as 10-15 minutes, and gradually increase the time as one becomes more comfortable with the practice. It is also recommended to practice Zazen for at least 20 minutes at a time to allow for a deeper experience.

In terms of the physical posture, there are several options for sitting positions, including the full lotus, half-lotus, Burmese, or seiza (kneeling with a cushion). The most important aspect is to find a posture that is comfortable and allows for a stable and upright spine. It is also recommended to have a straight back, with the chin slightly tucked in and the eyes lowered to a 45-degree angle.

While it is ideal to have a dedicated space and time for Zazen, it is also possible to practice in other settings, such as on a park bench or in a quiet corner of one's office. The key is to find a space and time that works for the individual and allows for a consistent practice.

In conclusion, while there are no strict rules about when or where to practice Zazen, it is important to find a quiet and dedicated space, a time that works best for one's schedule, and a comfortable sitting posture. With regular practice, Zazen can become a powerful tool for cultivating inner peace and insight in all aspects of life.