The process of metabolic recovery is an ongoing one, but exactly how long it will take to actually reverse insulin resistance depends a lot on the individual’s situation. Your HbA1C and your C-peptide levels will indicate your degree of insulin resistance. I have never heard that chromium is involved with insulin resistance or insulin sensitivity.
Insulin resistance is a combination of factors, depending on the organ in question, and I don’t believe it’s fully understood. Fatty liver clears up pretty quickly, and that depends largely on cutting out sugar from the diet. Insulin resistance in muscle requires healing of the mitochondria that were damaged by excessive oxidation. (This requires (a) lowering serum insulin, because elevated insulin activates a gene complex that blocks the body’s endogenous anti-oxidant mechanism from working; and (b) ketone production, because it is serum β-hydroxybutyrate that deactivates that gene complex, thus permitting the endogenous anti-oxidant mechanism to work again.) Insulin resistance of adipose (fat) tissue is partly determined by how full the adipocytes are of triglycerides, and partly by how easily that particular individual can form new adipocytes. Insulin resistance of the brain—Alzheimer’s disease, also known as Type III diabetes—can be reversed in the early stages, but past a certain point, damage to neurons becomes irreversible (though being in ketosis can still ameliorate the symptoms). The glycation of haemoglobin caused by elevated serum glucose can take around 90 days to resolve, that being the average life span of our erythrocytes (red blood corpuscles). Blood pressure starts to come down once elevated serum insulin stops interfering with the production of nitric oxide, but if there is atherosclerotic plaque, then the arteries remain stiff until the plaque can heal, which takes time. Until the repairs have caught up with the damage, blood pressure will tend to remain elevated.
All of these things depend on the degree of damage done to the bodily system in question, and people’s susceptibility to various types of damage varies both from person to person and within the same individual over time.
This lecture by Dr. Paul Mason might be helpful. He starts discussing insulin resistance at 13:20.