In the late 1990's, a professor of Physics named Len Fisher argued that there was an actual mathematical equation for determining how long you should dunk your Oreo for. Clearly, there was a media super storm following this insatiable news, for now we had cold hard facts to back this hot topic.
That mathematical equation in question here is called Washburn's Equation. The same equation is used in ink jet printing processes as they both have to do with one substance absorbing another through capillary flow.
Anyway, the team at MentalFloss.com says (now, this is based off science) that he proper dunk-time is a period of 3 seconds.
Check out the full "study" here.