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.
1 Homogeneous Mixtures-in which the two or more substances that form the mixture are evenly distributed throughout the mixture, e.g. vinegar is a homogeneous mixture of ethanoic acid and water.2  Heterogeneous Mixtures-in which the two or more substances that form the mixture are. Solutions-a special type of homogeneous mixtures in which one substance (called the solute) is dissolved in another substance (called the solvent), e.g. salt water is salt dissolved in water-in such a way that the salt no-longer exists as solid particles within the water.