The poskim do not give an exact amount of time for hagala; it seems to be a matter of several seconds.[2] Actually, the Shulchan Aruch[3] even alludes to the opinion that one should preferably not leave the utensil in for too long (to avoid a situation in which the expelled particles return to the utensil). It is difficult to argue with the logical intuition behind your assumption that the more an object absorbs, the longer it takes to remove everything that is inside. The Taz[4] seems to agree with this idea in theory, yet we still do not find a clear formula for how long the hagala should be and if – and by how much – the time increases depending upon the circumstances.
Let us analyze this halachic phenomenon, which we can develop only slightly in this forum. Some of the laws of the Torah are purely ritual in nature, and we should not expect them to depend on scientific factors or differing circumstances. For example, even if there is a correlation between species of birds being predators and their status as not kosher,[5] we would not say that a violent chicken would be not kosher or a kind vulture would be kosher. However, regarding something like kashering a utensil to remove the absorbed problematic substance, we might expect to need to be practically confident that we removed the requisite amount of the absorption.
It can be demonstrated that when the Torah gives instructions regarding how to perform kashering,[6] its intention was that if one follows the rules, he does not have to be concerned with the possibility that not everything was removed. Halacha indicates that one may assume it, and that suffices. This is a lenient counterweight to the following stringent nonscientific “assumption” regarding absorption. When a utensil was exposed to a substance in the presence of sufficient heat to expect that there was absorption, we halachically treat the utensil as if it became totally saturated with the substance. It is not that we really think there is actually that degree of absorption, which is in truth physically impossible, but since we do not know how much was absorbed, we halachically choose the worst-case scenario.[7] This stringent assumption applies even if the contact was for but a matter of a few seconds. (There is a machloket regarding whether there is some minimum time beneath which there is no absorption.[8])
It is true that there are sub-rules of hagala that change according to different circumstances. For example, if a utensil absorbed something while on the fire, hagala must be done while on the fire. If the absorption ensued via a lesser type of heat, then the heat requirements are correspondingly easier.[9] On the other hand, boiling water, if this is the required medium, is considered effective even if the temperature of the boiling water at the geographic site where the absorption occurred was higher than at the place of hagala (altitude affects the boiling point).
When we do make distinctions according to circumstances, it is often based on categories to which the Torah alludes. For example, Halacha distinguishes between the tendency of materials to absorb and the ability to kasher utensils made of different materials. Metals and wood are assumed to absorb and release particles normally. On the other hand, pottery is assumed to absorb a lot, such that normal hagala will not remove all that is required.[10] The commentaries find the source for the distinction in the Torah itself.[11] Poskim then discuss other, possibly unique, materials – such as glass – to evaluate into which category they should be put according to various characteristics.[12]
Regarding the matter of time, the Torah does not relate to different categories. Therefore, it should come of no surprise that once the requisite conditions for hagala are reached, it does not matter how many times or for how long non-kosher or chametz food was previously used in the utensil or for how long we performed hagala. It will not make a halachic difference if intuition or scientific evidence says that these factors have an impact.[13]