Thanks for asking your doubts on the curing time of cement on our community platform.
Portland cement takes 28days to achieve 99% of the desired strength regardless of the work nature and application thickness.
Applying the sealant before 28days on the cement layer will retard the complete hydration of cement by which it gains cement. This can form a weak section in your sculpture, which eventually could spall.
However, using rapid hardening cement instead of conventional portland cement and accelerated curing methods, the cement layer can achieve its full strength in a short duration.
To know about rapid hardening cement, click the article link given below:
To know about how to speed up the curing process, click the article link given below: