According to the provisions of Article 23 of the Company Law of People's Republic of China (PRC), a company shall go through the filing formalities when establishing a branch. Article 29 of the Measures for the Administration of Company Registration in People's Republic of China (PRC) stipulates the specific procedures and time limits for filing the establishment of branches, including the time limits for submitting application materials, administrative examination and approval and filing.
According to this regulation, the filing materials for applying for the establishment of a branch shall be submitted to the registration authority, which shall conduct examination and issue examination opinions within 5 working days after accepting the application. After that, the applicant shall submit supplementary materials within 5 working days after receiving the examination opinions, and the registration authority shall make a decision on approval or disapproval within 5 working days after receiving the supplementary materials. Finally, the approved branch shall put on record within 5 working days after the approval decision is made, and the relevant materials shall be received by the registration authority.
To sum up, the legal time limit for an agency bookkeeping institution to set up a branch for filing is 20 working days. It should be noted that this is only the legal time limit, and the actual processing time may vary according to the specific conditions of each region.