Does the patent invalidation application go to the Patent Office or the Reexamination Board? Or both. How long does it usually take to get the admission notice?

After the patent right has been granted and announced by the patent administration department of the State Council, if any unit or individual thinks that the patent right does not conform to the Patent Law of People's Republic of China (PRC) and its detailed rules for implementation, it may, from the date of announcement, request the the State Council Patent Reexamination Board to declare the announced patent invalid.

Invalid patent applications can only go to the reexamination board. After receiving the request for reexamination, the reexamination committee will conduct a formal examination. After formal examination, if it meets the relevant requirements, the reexamination committee will issue a notice of acceptance of the reexamination request. If it does not meet the requirements, it will send you a notice of correction, asking you to make corrections within a time limit.

Extended data:

Where the patentee requests to declare the patent invalid or partially invalid, it shall submit a Request for Patent Invalidation to the Patent Reexamination Board, explaining the reasons, and if necessary, it shall also attach relevant supporting documents and the facts on which it is based.

The request for invalidation and relevant documents shall be made in duplicate. Before the Patent Reexamination Board makes a decision on the request for invalidation, the person requesting invalidation may withdraw his request.

If the request for invalidation of the patent right does not conform to the prescribed format, the claimant shall make corrections within the time limit specified by the Patent Reexamination Board; If no correction is made within the time limit, the request for invalidation shall be deemed to have been withdrawn.

Baidu Encyclopedia-Patent Invalidation Program