Certificate of Negative Result of Nucleic Acid Tests

I am taking a flight from Kuala Lumpur to Guangzhou on Dec. 28, 2020 and need to submit my health declaration 3 days before departure. That is, on a working day from 25th to 28th Dec. But 25th Dec is Christmas Day and 26th/27th Dec is weekend.

May I know what should I do? Can I submit on 24th Dec 2020? 24th Dec is 4 days from the date of departure. Please advise. Thank you