Final answer:
Wet plaster should be protected from freezing for 48 to 72 hours to prevent structural defects.
Step-by-step explanation:
Wet plaster should be protected from freezing for at least 48 to 72 hours. Freezing temperatures can cause the water in the wet plaster to expand, leading to cracks and other structural defects. To protect wet plaster from freezing, it is important to keep the temperature above freezing and provide insulation or temporary heating if necessary.