https://webapp.es2.immd.gov.hk/smart.../menuPage/faqsQ3. What if the appointment booking quota on the date I prefer has already been filled?
Appointment booking system provides booking services for the following 24 working days. If the quota for your preferred day has been filled, you can make an appointment on another day. Quota of the 25th working day will be released after midnight. Besides, there are limited walk-in quotas at Registration of Persons Offices. Subject to the availability of quota, you may attend a Registration of Persons Office in person for a walk-in tag.