Usually around 3-4 weeks, but the length of drying time will vary a lot depending on seed size and thickness and impermeability of the seed coat. It could be from 1 week (for tiny seeds with thin seed coats) to up to 2 months or more! (for larger seeds with thick, water-impermeable seed coats). We recommend always spreading the seeds in a thin layer and mixing them occasionally during the drying process, to ensure the seeds dry evenly. Then measure the equilibrium relative humidity (eRH) of seeds sealed into a small container with a hygrometer to ensure seeds are dry enough for storage.