I haven't seen the link so I don't know what "nutritional ketosis" is and I don't understand why it would take 2-6 weeks to get back into ketosis after a cheat.
But I can tell you from my personal experience that when I eat enough carbs to get me out of ketosis, it usually takes me 3 days, 4 max to get back into ketosis. 3 - 4 days of clean eating and lots of water. But I also exercise 5-6 days a week so that may have something to do with it. I know the signs my body gives me when I'm in ketosis so I don't have to rely on keto-stix. When I do use them they always turn pink or purple.