Yes. Joe is closest to the truth. It is an ongoing process. I have personally made progress and can feel that there is a lot more to go. I do think the word "achieved" is appropriate.
wpg makes a good point: small circulation is 'open' for everyone alive, and eventually it will happen naturally for you, and you can just sit there. But wpg, you won't win any friends by implying that you know more than the two most widely-acclaimed teachers of qigong on Earth. Both Dr. Yang and Master Chia teach this qigong in excellent ways. They are rare open teachers who have for the first time given clear and detailed instructions, which you might want to revisit.
Once you get into the right posture, qigong just happens.
This is misleading. Eventually, once you have done the necessary work, this is true. But not before.
Qi gong means "energy practice" or 'skill". Gong is short for Gong Fu, which translates to "effort and time". The purpose of practicing small circulation qigong is to widen the flow of energy through the Conception and Governing vessels. In that process, you also open three areas in the back that have a very narrow channel in most people. This requires practice (time and effort). If you don't practice qigong, then as you age, these narrow places can almost close entirely. These are the three "tricky gates". Your energy will be low, and your health will fade. Many people later in life are sedentary, and this results in poor circulation through the small circ. The bones on the lower spine can even fuse together in some folks. If you have a moving practice, and you have widened the small circ, this wont happen.
Qigong IS a cerebral practice, especially at first. It is not Zen, where you just sit there and allow your cultivation to happen. If you don't understand qigong theory, your practice will be in vain. You can practice for a lifetime incorrectly and gain limited benefit, or you can practice with understanding of the theory and progress quickly.
The YI leads the Qi. Your intention leads your energy. So, yes, you need healthy posture and alignment, but you also need to lead the qi with the mind. Energy follows consciousness. Once the small circ is open, it can continue to develop. After a lot of progress, with diligent effort in this area, the changes that you affect will become long-lasting. THEN, you can just sit there as wpg suggests.
Points. Visualizing certain points along the way is a master's trick to get you to make progress safely, while avoiding the three tricky gates. Because if you think about those places, you lead more qi to them, and the problem gets worse. The trick with using specific points is that a student learns to focus on a safe acupuncture point along the small circ, beyond the tricky gate, so he/she safely opens the area "below" with no risk of trouble. Once you have opened the small circulation, you will understand and feel this, and then, yes, you can forget all the theory. The theory is like a ladder. Once you have climbed up to where you need to be, you no longer need the ladder.
In some traditions, Zen, kundalini yoga, etc. people achieve opening the small circ through other means. Whatever works for you.