How fast candy dissolves in water depends on how much candy is used, the temperature of the water, the composition of the candy and its surface area. The duration can range from minutes to hours or even longer. Candy is composed mostly of sugar, which is very soluble in water, so although the dissolving process should not take long, an exact figure is impossible to give without knowing all variables.
The less candy one uses, the faster it dissolves in water. The surface area of the candy is also a factor. A sugar cube dissolves slower than granulated sugar of equal mass because the granulated sugar has more surface area exposed to the liquid.
Adding heat to the solution is the easiest way to expedite the process. If the water is hot enough, the rate of solubility increases dramatically. Applying pressure in the form of stirring or shaking also hastens the process.
Although the candy seems to have taken a new form once dissolved into water, the substance has not changed. A chemical reaction does not occur when a substance changes states from solid to liquid, and no new substance is created. If the sugar water evaporates, all the sugar from the candy is still present.