It is advisable that you apply for a visa one month before
your intended date of entry into China.
For instance, if you plan to
enter China on July 1, the best time to submit your application would be around
June 1 (counting working days only).
Please note that the validity of some visas is equal to or shorter than one month. In that case, you may apply for the visa around two weeks before your intended date of entry into China.