If the time required to wait between eating meat and milk is based on the scientific definition of digestion, why don't we ask today's experts and set a defined time for everyone instead of different people following different customs?
For Ashkenazim at least, the halacha is like Tosafot, that once one finishes the meat meal, if he starts a new meal he may consume dairy. However, in the common case, people follow their minhag of how long to wait. See the Rama in Shulchan Aruch Yoreh Deah 89:1, as I've seen it traditionally understood -- that he paskens like the יש אומרים that one needs not wait, but that it is a מנהג הפשוט במדינות אלו to wait, rather than a decided halacha -- such that in cases of great need, this minhag may be relaxed.
If so, the science won't help.
Waiting six hours is not based on the scientific definition of digestion. The Talmud (Chullin 105a) says that one must wait from one meal to the next. There is a disagreement among the Rishonim if that actually means from one meal to the next, or if it means the amount of time between the morning and evening meals, which would mean approximately six hours. See YD 89. The reason for the wait according to these Rishonim is either that fat/grease from the meat that is in one's throat emits a meat flavor into one's mouth for a long time (Rashi) or that for that amount of time we are concerned that small pieces of meat might be stuck between one's teeth (Rambam). Neither of these reasons say that these issues last exactly six hours, but rather that the Sages drew a line at six hours, and neither of them have to do with digestion per se.
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