Most pine decks need to be stained right away. You need to repeat this treatment at least once per year. If you do this religiously you will have a nice looking deck for many years assuming the deck was properly built.
When a pine deck dries it shrinks. When it gets wet it swells, but normally only the surface gets wet from a rain shower. So now the surfaces expands, but the center of the board does not. This nonuniform expansion and contraction is what makes the boards crack, splitter and warp. Keeping the board sealed helps prevent the damage.
Some pine decking boards are impregnated with paraffin wax at the same time the preservatives are added. This wax goes to the heart of the board and prevents moisture penetration. In effect pre-sealing the board. However, the weather removes the wax from the surface of the board overtime. With this board you need to wait a few months before you stain the deck since the wax will prevent penetration of the stain. After a few(typically 3-6) months the top thin layer of the wax will burn off and a stain needs to be applied to reseal the surface. This needs to be repeated about every 3 to 5 years.
One draw back to the paraffin wax is excessive shrinkage which can leave gaps between the boards that are larger than you need for good drainage. It can also cause cupping. The only way to insure this doesn’t happen is to dry the boards before you install them. The only practical way to do this is to buy boards that have been dried by the treater. This is called “kiln dried after treatment” or KDAT. These boards are more expensive and not available in all areas, but in my 18 years of building decks I have never used a finer pine decking board. They are well worth the extra cost.