about 2 yearsProperly stored, a package of bouillon cubes or granules will generally stay at best quality for about 2 years. To maximize the shelf life of opened bouillon cubes or granules, keep package tightly closed.
Since Kakashi and Obito were 13 during the Third Shinobi World War and 31 during the Fourth, it should be an approximate 18 years between the two wars. It lasted around three days, maybe five if one includes the declaration, amongst other things.
However, the fusion only lasts one hour for mortals, even if the fused being removes the earrings.