Soap is a mixture of crystaline fatty acids, semicrystaline fatty acids, and water and glycerine surrounds those partially crystalized particles. This means that things can migrate around and re-arrange into more stable "assocciations".
The result is that the soap become less soluble in bulk while often becoming more soluble on the surface, if that makes any sense -- it will lather better from the surface, but the bulk of the bar has less water in it, so it resists dissolving more. Harder, waxier bar that lathers better and lasts longer.
Saponification can continue for quite a while, too, at a very slow rate. This will reduce the alkalinity, making the soap milder too. Rate and amount dependent upon superfat, initial oils, temperature, and so forth, but after six weeks everything should be more or less in equilibrium. Except for high oleic soaps, which can take a year or more to get to a fully stable state (Castile, for instance, but also soy, canola, safflower, etc liquid oils).
Some (if not all) of the "granular" character will vanish since it's a result of soap in a more or less crystaline state surrounded by oil -- as saponification finishes the fatty acid salts will rearrange quite a bit, reducing the effect. Probably be visible forever, but I don't think people pay all that much attention to what soap looks like while they are showering with it.
DeeAnna posed a detailed explanation of soap cure, it's worth looking up.
