"If these (seeds in vapor proof pouches) are immediately placed in the freezer, what is the optimum time they could be kept and still get a good germination rate?"
According to Suzanne Ashworth in her book - Seed to Seed - "Seeds of all species can be stored for many years with almost no loss of germination, when dried to about 8% seed moisture,sealed in an airtight container and frozen. Seed stored using these techniques will maintain their viability for up to ten times longer than normal germination rates. A quick and easy test is that seeds will break instead of bending when folded, if their moisture is 8% or less. Also hard shell seeds, such as corn or beans, will shatter instead of mashing when placed on concrete and struck with a hammer. When retrieving seeds from frozen storage, always allow the sealed jar (or heat sealed pouch) to reach room temperature before opening. When taking seeds from the container, reseal the jar or moisture proof pouch quickly, so that the seeds will retain as little moisture as possible."
All of Seed for Security's seeds are carefully dried and are ready for freezer storage. I do use the methods that Suzanne Ashworth recommends. Some years ago I planted mixed baking beans that my grandfather had stored in his freezer for 22 years. The germination rate surpassed other beans seeds that I had bought from a trusted company.
I hope this information is helpful to you.