To correct asymmetrical posture, we need to change our muscles and tendons first as they are the main structures that keep our body intact and in position. This means that we need to know how long it takes for muscles and tendons to change in order to bring the skeletal parts back to its normal position.

In the first paper below, they studied the extent to which exercises can change healthy tendons. It is said that the tendon gradually changed when the participants exercised for more than eight weeks at the intensity of more than 70% of the load that the tendon can withstand (70% of your weight based on Achilles tendon). They also suggest that muscles change much faster than tendons.

The second paper states that the Achilles tendon eccentric exercise (repeated twice a day for 3 sets x 15 times, more than 6 days a week) for 12 weeks was effective in solving the problem of Achilles tendon. So if we put it together, it takes about eight weeks to change a healthy tendon and 12 weeks to change a painful tendon.

However, how much change do we need to see in the tendons for it to physically pull bones and change the structure? This will be different for each person. Surprisingly, people who have never exercised before tend to change their body shape faster than bodybuilders. Perhaps, it is because it takes longer for bodybuilders to develop inner muscles to overcome the strength of their large muscles that have developed over time. Inner muscles are the ones that hold the bones in place and are considered more important for postural correction.

For example, in the case of a bodybuilder with extremely developed thigh muscles and anteriorly tilted pelvis, it may take relatively longer to develop the strength of the inner muscles (core, gluteus medius, etc.) enough to overcome the strength of the thigh muscles and tilt the pelvis backward.

References

Bohm, S., Mersmann, F., & Arampatzis, A. (2015). Human tendon adaptation in response to mechanical loading: a systematic review and meta-analysis of exercise intervention studies on healthy adults. Sports medicine-open, 1(1), 7.

Beyer, R., Kongsgaard, M., Hougs Kjær, B., Øhlenschlæger, T., Kjær, M., & Magnusson, S. P. (2015). Heavy slow resistance versus eccentric training as treatment for Achilles tendinopathy: a randomized controlled trial. The American journal of sports medicine, 43(7), 1704-1711.