I mean really, if any of us was "enlightened" enough to be able to interpret a good portion of our body signals we would have never eaten those glazed donuts and other crap that brought us here in the 1st place. Add that that most likely none of us has ever experienced "real hunger".
One thing that will give you some insights on the sequence of event that occur while fasting is to read the Detox Stages in the FAQs at the top of the page. If I'm going through all the trouble and in many cases social isolation since many of our interactions with other revolve around food, I'm just gonna go for broke and reap some real cleansing benefits at the cellular level which only begin to happen after around 2 weeks when the body has expelled the causative agents and the system starts scouring the cells for damaged tissue, In short for me I consider 21 days the minimum worth doing though I really push the envelope and do the 40 days anyways.
You know to be honest I could not come up with what determines the end time for me on the MC. One guide that I've observed is that the cleansing cycles appear to go by in 7 days increments. What I will tell you is that personally I've never experienced what I would interpret as "real hunger" in my dozen+ 40 day fasts. For the last 3 or so fasts I have switched things around a bit. I will do no less than 21 days MC by the book then I switch to veggie juice for the remaining 29 days +/-. This "Switch" was something that came about more by accidental circunstance than anything I consciously planned. It came about cause I was on a deadline job and left the house one day somewhere around day 30 I left the house and forgot my lemonade. I figured, no big deal, one day on water would be fine. As the jobs pressures and activities wore on by mid afternoon I started getting a bit wonky and I just had to be able to carry on so with much trepidation I went to a local juice bar and had a green juice. I drank it real slow worrying that after 30 days +/- it might make me sick but much to my delight I got this great feeling of well being and energy so I finished out the fast on veggie juices and have done same for the last coupla fasts.
It simply makes good logical sense to me that you do a good 21 days getting the crap out of the system and then with the veggie juice you are infusing your system readily assimilable mega nutrition, live enzymes, vitamins, minerals etc. In addition since the system is pretty clean from the MC it will really be able to absorb all this great nutrition provided by the veggie juice. Of course they system will also continue to detox with the veggie juice.