Here’s my theory. Insulin action time is a fixed value. It doesn’t change. Since insulin is injected into an environment that includes factors that “push back” the effect of insulin, it’s not so easy for us to measure.
You can’t simply observe the movement of blood glucose and then attribute that effect to insulin alone. There are a host of other things that interact with insulin including cortisol and adrenaline.
Diabetes is a dynamic disease. It’s simplistic to only rely on fixed formulas to dose insulin. Insulin resistance goes up and down, even in non-diabetic individuals. One poor night’s sleep, for instance, will raise insulin resistance in all people, including non-diabetics.
No, I don’t experience radical shifts in insulin resistance but I do live with small changes day to day and milder trends over a few weeks that causes me to make regular changes to my basal rate and insulin sensitivity factor settings in my automated insulin dosing system.
You have not shared any of the context for your questions. Are you diagnosed T1D or T2D? How long have you lived with diabetes? How old are you? Is it possible that you are experiencing a slow onset form of T1D known as latent autoimmune diabetes in adults or LADA?
What kind of diet do you consume? Does your diet include bread, noodles, rice, potatoes or highly processed foods like breakfast cereals or “energy” bars? Do you drink carbohydrates like carbonated beverages or juice? Do you eat three meals a day? What about snacks?
What is your exercise regimen, if any? How well do you sleep? What stresses do you live with every day?
Have you asked a doctor or other medical professional these questions? If so, how did they answer?