The answer to this question is almost as varied as the individuals who ask it. Everyone responds differently with numerous contributing factors such as body type, age, diet, smoking and drinking habits, consistency and mental attitude to name a few. No matter, you will see some results right away, however, these are only temporary so you will need consistent practice over time to realize stable gains.
Keep in mind that the Innerwear is a passive extender, so it is highly recommended to engage in a number of methods and techniques that would include at least some manual jelqs and stretches. The Corkscrew would be a good addition to your training routine as well as some other higher intensity short-duration exercises such as hanging to induce a state of deformation to initiate growth.
Gains will best occur with a multifaceted approach for which the innerwear is effectively used as a passive extender 24/7. This enables the penis to heal in the extended condition which is helpful to cement permanent gains.