A safe and recommended approach is to initially limit sitting to half an hour, or two half-hour segments, in as relaxed a manner as possible. This refers not only to your inner, but also your outer environment. For beginners, if the mind is burdened with outside concerns, it may be better to relieve some of these burdens before sitting. For this reason, it is best to sit early in the morning, before dealing with the problems of the day. Sitting times may be increased with experience. But people who do tso-ch'an for extended periods may become so engrossed in their effort that they may not recognize their tensions. This frequently exists because their minds are preoccupied getting results. So to work hard on tso-ch'an means to just put your mind on tso-ch'an itself. If you can just do that, there is no need for tension to arise. On the contrary, deeper relaxation, and calming of the body and mind should result.

The Tso-ch'an of "Outer Paths" 外道禪