I worked up slow, 1.5 days at first.

My max was 4 days, I had to stop because of back pain from an old injury, healing pain maybe but it was too much.

If you have enough fat, the body can burn it off to make water from the oxygen you breathe and the hydrogen in the store fat.

I was not moving much on these days either, little walks, housework and meditation mostly.

The best time for me to start was about 6h before bed.