I am a Swedish Jew and want to know why we wait specifically 72 minutes after eating meat/flaysh before eating miklhigs. A lot of people say it is an hour, but my understanding is that a one-hour waiting time is actually Rabbeinu Tam (though is so frequently mis-cited as Northern European custom that you can find that everywhere on the internet), and the proper Swedish custom is 72-minutes. Why 72 minutes specifically?
See the באר היטב in Shulchan Aruch Orach Chaim 186, s.q. 8:
עד שיתעכל. ושיעור עיכול בשאכילה מועטת הוא כדי הילוך ד' מילין והוא שעה וחומש וכת' המ"א נ"ל דהאי עיכול תחלת עיכול הוא דסוף עיכול הוי' עכ"פ ו' שעות
Until [the food] is digested. The measure for digestion for small eating is the time it takes to walk 4 mil, and that is one and one fifth hours. And the Magen Avraham writes "It appears to me that this digestion is the beginning of digestion, because the end of digestion is regardless 6 hours.
My dutch wife tells me that the custom there is one hour, but her parents keep six so she may not be exact about it. If the Swedish custom is the wait 72 minutes, it would seem to be around this concept of waiting until [that stage of] digestion begins, instead of when it ends.
(The context in Shulachan Aruch there is the length of time one can still say the blessing after eating, not about waiting between meat and milk).