You should start wearing a posture corrector for about 15-30 minutes a day and gradually increase the time as your body gets used to the corrected posture position.
Wearing a posture corrector all day is not recommended, as it can be painful and uncomfortable and may lead to muscle dependency or weakness. For the best results, wearing the posture corrector for at least two hours every day is recommended, but be sure to give your body breaks and not wear it continuously for too long at a time. Combining a posture corrector with exercises and stretches is also important to strengthen the muscles necessary for good posture.