For me, 3-4 days. But I also don't go really low carb. I'll still eat a piece or two of fruit a day - an apple with protein and perhaps berries or a grapefruit. I also eat veggies. I just stay away from breads, cereals, rice, pasta, etc. they all act like sugar to my cravings,
For me, it comes and goes, it's never gone completely, my husband can tell right away that I've not had my dark chocolate for the day, for example. Don't be fooled by the books and ads, real life tends to be different. And think about this, you have to do this the rest of your natural life, or at least until assisted living.
The 3rd day gets much better for me but still rough the 4th day is my turning point. But the trick for me is no matter how bad it gets I can not have any more sure/simple carbs dont cave in. Yes I have fruit but have lots and lots of protein it really helps coping with the sugar lows/shakes. It really is so addictive, and it is hidden in so many products we eat daily and not even aware of it.....Stay strong!!!! You can do it.