Yes, admin has complete knowledge about the requirements, but I believe that most of the users whose activity was frozen are having unfrozen activity on their profiles now. The reason could be an internal update on the requirements.
In reality, each user is different in this case. The requirements (number of posts, total time spent online and a still unknown amount of karma, when the administrator finally implements it on the forum) are not always the same, it depends, for example, on whether the user is a Full Member or Legendary. The higher the next rank, the higher the requirements to achieve it. Therefore, the time needed may vary, especially at higher ranks.