I do a lot of stain work and I would wait three to four weeks if possible to stain after purchase. Keep in a dry, weather proof area if possible-a garage, shed or workshop. If you have to keep the lumber outside, elevate it on some 4 x 4 runners and expose it on clear days.
Scientists say that solutions are homogenous systems. Everything in a solution is evenly spread out and thoroughly mixed. Heterogeneous mixtures have a little more of one thing (higher concentration) in one part of the system when compared to another. Let's compare sugar in water (H 2 O) to sand in water. Sugar dissolves and is spread throughout the glass of water. The sand sinks to the bottom. The sugar-water is a homogenous mixture while the sand-water is a heterogeneous mixture. Both are mixtures, but only the sugar-water can also be called a solution. Pretty much. Solutions can be solids dissolved in liquids.
A pure substance contains only one kind of molecule, and a mixture is a combination of two or more pure substances. Distilled water, aluminum foil and table sugar are each made from only one type of particle. However, salt water is a mixture because it contains salt as well as water.