Can I get a health certificate on Saturday?

You can't.

Generally speaking, the business of handling health certificates is generally carried out during the morning and afternoon working hours from Monday to Friday. Generally, health certificates are not issued on Saturdays, because this is the weekend, and medical institutions generally arrange staff to have a rest or rest. Enterprises and institutions can flexibly arrange weekly rest days according to the actual situation, but generally do not apply for health certificate business on Saturday.