I use the 1" per year rule for woods in stave or log form with the bark still on. But in board form, it is much quicker. You can dry 1" thick boards in a couple months or much sooner if you force dry them.
I'd get it down boards that are 1/4" thicker and a couple inches longer than my maximum intended use, coat the ends with wax or shellac, sticker the boards (stacked with small boards in between layers to allow airflow), then store them place them in a steady relative humidity.
As shamus said, if it is sold as lumber, it might be air dried already.