Guangzhou can apply for a health certificate at the weekend.

You can't. You can't get a health certificate on weekends. The working hours of public institutions and administrative organs are generally 8 hours a day and 40 hours a week from Monday to Friday. Saturday and Sunday are weekly rest days, and generally do not go to work. Therefore, the parties concerned can't apply for health certificates on weekends, but should do so on working days every week.