Once you have unsealed and opened your panko breadcrumbs, they will stay good for 1 to 2 months. This time frame of how long your panko breadcrumbs will stay edible and safe to eat after opening very much depends on how they are stored. Store bought panko breadcrumbs will last longer than homemade. If your panko breadcrumbs are in a tightly sealed container or bottle, they will stay fresher for longer.