If they stay sealed, cool and dry, could be years. Also depends on the specific seeds. Some seeds (narrow-leaved campion) have a viability of 30,000 years. Some (cottonwood) have "transient viability" - 24 hours. Patriot Seeds website says 5+ years.
Maybe the best part is that these are from Indiana, and therefore acclimated to Indiana soils and climate.
As an experiment two years ago we bought dried black beans at Wal-Mart and tried growing them. Not only did they produce good plants, but the beans from those plants produced good plants the following year.