It's best to stand a pile several times a day.
Twice is appropriate. Standing pile means that the body is as still as a stake, and its purpose is to be as stable as a stake, not as still. It is an important part of China Wushu system. Martial arts schools of past dynasties, such as "Ma Bu Zhuang", are valued by practitioners and regarded as basic training in Shaolin Wushu and some southern boxing schools.