Q: HOW LONG WILL THEY HOLD ON TO THE PACKAGE BEFORE IT IS RETURNED TO ME?
A: If the address does not exist, it will not be held and returned immediately. If it is an old address of someone that has moved, it most likely will be forwarded or returned, immediately. If it is a valid address and it is known that the person does not live there, it will be returned immediately. If it is a valid address the carrier may leave a notice, or the package if the name is not recognized. It is not really possible to answer your question as you do not say what is wrong with the address or why you would think that the package would be held at a Post Office.