Fasting starts when you finish eating. It can take up to like 8 hours for food to even get passed your stomach and small intestine, so you’d be waiting quite a while.
Also how would all the ratios make sense, there’s only 24 hours in a day. Doesn’t need to be overcomplicated, the clock starts when the fork gets put down.
If I’m not eating, I’m fasting, so I count after my last bite. It doesn’t really make sense to me to count digestion as eating, especially since it takes so long to move through your system and fully digest (up to 8 hours usually). In my opinion, fasting is about intake so if it’s just digestion and you’re not taking in additional food, you’re fasting.