You are always welcome. Legal analysis: anytime. Since the date when the patent administrative department of the State Council announced the grant of the patent right, any unit or individual may request the Patent Reexamination Board to declare the patent right invalid if it considers that the grant of the patent right is not in conformity with the relevant provisions of this Law.
Legal basis: People's Republic of China (PRC) Patent Law.
Article 42 The term of patent right for invention is 20 years, and the term of patent right for utility model and patent right for design is 10 years, counting from the date of application.
Article 43 The patentee shall pay the annual fee from the year when the patent right is granted.