How much time is left?

In the first 3 days, the body is still using energy from glucose. After that, the liver starts processing body fat, in a process called ketosis. After 3 weeks the body enters a "starvation mode". At this point the body "mines" the muscles and vital organs for energy, and loss of bone marrow becomes life-threatening. There are examples of hunger strikers dying after ~50 days of strike.