Ive germinated seeds that were over 10 years old that had been just sitting in a drawer in a baggie. (about 70% germination rate, normal rate for me is 100%) As long as its not hot, not direct sun and such they should last quite awhile. Some people put them in the freezer to keep them viable even longer.
Freezer almost a indefinite amount of time. Scientists have recovered seeds from tombs or crypts that are hundreds of years old and germinated them. Most of the advanced nations have some sort of long term seed storage to preserve diversity and they keep it on very cold storage.