It really depends on the species of plant as to how long the seeds remain viable. Given that the seeds are pelleted, it sounds like they are likely annuals in which case they probably have good (multi-year) longevity.
Well, why don't I just ask - what are the seeds for?
Is there no info on the seed packets, or even get in touch with the supplier's, it's difficult to know the best advice as things will depend on your zone, where and how you store the seeds and even ask, do you wish to do a later sewing of the same seeds like I do with carrots, peas ect so I dont have a glut of stuff needing picked / harvested all at the same time.
Can you say what type of seeds you have, some seeds are good for another year and others are best used the same year.
Good luck, Weenel.