Kept perfectly dry, these chemicals will last almost indefinitely. I have some phenidone that is about 20 years old and is still good. Glycin is the only developing agent I know of that deteriorates quickly (in less than 2 years). If your environment is damp, however, developing agents may die much more quickly. I've heard tales of phenidone deteriorating in as little as three years in a humid environment. If metol starts clumping it is not a sign of certain deterioration, but I would treat it as suspect.