Hey FastGuru - yes those statements are correct. To clarify - we never reach real ketosis obviously unless we are not able to properly convert proteins to glycogen properly which is a life threatening state. I was being lazy using the word "ketosis" as it is easy for most people to understand.
Here is a highly unresearched topic that I believe will someday be on the frontier of understanding in many areas including health and elite endurance athletes. The best way to teach our bodies how to burn higher percent of fat stores versus glycogen in day to day movement is by training fasting or at least a glycogen deficient state. Most people don't really think of fasting / intermittent fasting as a type of training, which it is. One benefit is it teaches our body how to use ketone fuel more efficiently and can integrate these in sooner than an untrained person.
We all know the feeling of bottoming out on the glycogen scale where our livers and muscles reach that 50% threshold and the remaining part will be saved and used only when mandated by the body. All replacements now come from stored proteins converted to glycogen. This time of this state varies for people depending on two three main factors (amongst others). 1 calories burned (specifically glycogen) 2. Muscle Mass - how much glycogen fuel we are holding 3. Training.
Number three is the most unstudied topic and why I say it takes me 5 days, sometimes 6. My body over time has become effecient at using ketones through the use of intermittent fasting and fasting over the years I have measured through ketone strips to subjectively see if this transition was taking as long as I was feeling.
My guess is for someone who is highly untrained at using ketones as fuel will 1) feel worse and 2) reach the ketogenic state much quicker as the body's cells are not used to breaking down this stored food for energy quickly. These ketones are used of course by everyone, but again...this is more of a theory through personal experience and do not know all the facts.