The graph of the effectiveness starts low, rises fairly quickly after that 15-20 minutes to that 2 hour
peak, then then gradually tails off. You may want to check on the 6 hour
duration, many insulin experts will recommend you use 4 hours as the length of the insulin duration. So your blood sugar rises because of the immediate release into your system of the carbs in the ice cream, flooding your bloodstream with carbs, and the insulin takes a bit to get working.