I assume that you are referring to the atrophy that occurs through the use of anti-androgens such as spironolactone or aldactone.
Temporary atrophy occurs pretty quickly. In other words your sperm count and testosterone production drops within a few weeks. This can be detected through manipulation of the testes. They will feel shrunken when compared to the size before use of AA's. Additionally, ejaculation and semen will be reduced, erection will be debilitated, and there will be a loss of libido as well.
The atrophy becomes permanent, I.E. chemical castration, after approximately nine months. Following that, even stopping the use of AA's will not produce an increase in sperm, testosterone, or libido and the ability to have an erection will be severely impaired.
-Sandy