Q: How many times it take for a Patent to be "free" when it is not exploited?

A: You should clarify your question. The patent remains enforceable for its entire life. Absent unique circumstances, this is generally 20 years from the earliest filing date from which the patent claims priority. Feel free to reach out to me with further questions.

A: This is a very common philosophical question or a public polity in patent law. Since patents are made to promote the progress of science by securing for limited time to inventors the exclusive right to the inventions, what happens when the inventor does not do anything with his invention?

Suppose that an inventor invents a product or a service that would make this world a better place. Does it make sense to let the patent owner not to take advantage of the invention and make and sell the product to the public, and to let the patent owner prevent others from making and selling that product? It seems like the patent owner is abusing the system.

In some countries, the government says: "well, the invention belongs to the patent owner, and if the patent owner for whatever reason does not want to make and sell it, that it the patent owner's right." In other countries, the government says: "well, there is a useful invention, and if the patent owner does not use it, then others should be able to make it and sell it for the benefit of the society; the government will not invalidate the patent, but will force the patent owner to license the patent to interested parties for a reasonable fee."