Final answer:
Alginate impressions should be stored in 100% humidity for up to 12 hours before pouring to maintain accuracy; however, it is best to pour them as soon as possible to avoid distortion.
Step-by-step explanation:
An alginate impression material must be kept in 100% humidity for up to 12 hours before pouring. Alginate is a hygroscopic material, which means it can absorb moisture from the air. This property necessitates its storage in 100% humidity to prevent any dimensional changes that can affect the accuracy of the final dental cast. However, best practice recommends pouring the alginate impression as soon as possible after taking it to avoid any potential distortion.