How long the regeneration phase lasts depends on several factors. These include, for example, your personal training level, the intensity of the exercise or your age. As a guideline, which can be seen as the optimal regeneration period, a period of between 48 and 72 hours between the two training sessions is generally considered to be acceptable. These can also be shorter. Important: It doesn't work without breaks and regeneration!
However, this is not a license to do nothing: This advice only applies to the muscle groups that were last used.