I'm no expert either, and I don't know how long it takes to go into "Starvation Mode". But I do know that when you are on extremely low calorie diets, you can lose weight, but you will be losing MUSCLE as well as fat, because your body will literally begin to eat itself, including muscle and fat and eventually organ tissue.
Also, since your body perceives it is starving, it slows your metabolism down as far as possible, as it is desperately trying to hold on to as much fat, muscle and organ tissue as possible so it will survive as long as this "starvation" is happening to it.
Yes, people lose weight, but they rarely keep it off for long, because once they stop eating the super low calorie diet, and begin to eat more regularly, their metabolism has slowed down so much that they gain weight rapidly on fewer calories than before. The body is now trying to "store up" as much fat as possible so that it will be ready for the next starvation. It doesn't know another one might not be coming!
That is why people who get gastric bypass surgery must take volumes of supplements for life. Also why some seem to lose just so much weight, then stop even though they eat so very little. And even why some gain weight after having lost it after surgery.
Not to mention: loss of hair, and many other deleterious effects starvation has on the body, some of them irreversable, makes starvation diets a bad idea, IMO.
I have researched all kinds of diets and have considered the surgery myself in my many attempts to lose weight, and this is just some of the information I found. Hope it helps.