Because I have already used a therapeutic dry fast many times, I also tried to answer this question. I have never been rewarded because there is no info about this specific subject in any literature; even Filonov's book red by me in its original language, neglects this subject.
I believe that our body always requires not less than 2-3 days to create a state of ketosis, and it does not matter if it is during a dry or water fast.