I have been taught somewhat differently. In general, the waist controls the legs as well as the arms, and in most cases, the weight shift is accomplished as the waist turns. However, in Wave Hands like Clouds, the weight shift is accomplished earlier. After stepping out with the left foot, the waist turns to the left and the hands rotate. At the same time the weight shifts to the left foot so that by the time the left hand starts to go to the left outside the body, the weight is totally shifted to the left and the right leg is closed.
This approach actually has some advantages. If necessary, weight can be shifted to the right leg and the left leg step out before the waist is fully rotated to the left. Even if there is no need to step out, some weight can be shifted to the right as spiral energy is led from the legs up through the waist and out through the left hand. This also lets the body accomplish a small move to the right to offset the extension of the left arm and hand.
When turning the waist to the right, the weight is shifted to the right leg by the time the right hand moves past the body, so that the left leg can extend out, offsetting the extension of the right arm and hand.
In most of the other movements, the waist controls the shift of weight, so that the weight is shifted totally when the waist has almost stopped turning. There is only a small residual turn of the waist to move the empty leg to where it should be placed.