When doing zhan zhuang practice, people often place their focus on qi. This may be over-emphasising one aspect of zhan zhuang. Although standing does produce a sense of qi, it is a natural phenomenon and a reaction of the body during practice. Feeling it but not being able to control it means you cannot bring it forth and utilise it. Although Taijiquan is a practice that cultivates internal gongfu, "internal" is not only qi; the bones, muscles, tendons and ligaments etc and the viscera are also "internal" aspects.
From the beginning Taijiquan practice involves all these things. So zhan zhuang first, regardless of qi, must involve loosening and extending your muscles and bones etc with correct alignment. The main areas to loosen and extend being the shoulders and kua. The sign that the basic loosening process is in place is when you are able to hang the two arms and maintain a half circle position for an extended time. The length of time you can hold depends entirely on the degree of looseness and relaxation you have achieved. The sign that the kua is released is when the body's power and weight are able to go downwards to the ground through the muscles at the back of the legs (not the muscles in the front of the legs that causes knee pain and injury).