Wood moves. Temperature and moisture can cause it to shift, primarily across grain and not so much along the grain. Consequently, when you acquire wood and plan to use it in a noticeably different environment it’s advisable to give it time to acclimate. Once it’s settled you can square it up and not worry that over the course of the build it will shift.
Since plywood is stacks of thin veneer where alternating layers are glued in a cross grain structure, it’s much more stable. Remember, the longitudinal fibers don’t shift much from heat and moisture. By alternating the direction of grain in plywood layers, the resulting wood product is much more stable. Hence, there’s little concern with having it acclimate before using it.