New NICE guidelines.

I think the reason why the postprandial reading was moved from 2 hr to 90 minutes is to provide a slightly better indication of the peak amount of glucose in the blood following a meal. It seems most of us start to convert the simple carbs into blood glucose around 15 minutes after the meal, and for a normal GI meal it will peak around 1 hour after the meal. A Low GI meal, or one with high fat content will digest later, and it used to be that the 2 hours test was a resonable guesstimate of when the peak occurred (our diets have changed a bit since those days) It is not an exact science, and varies according to what is in the meal, and what your meds are doing. My DCN advised me (T2D) to do a 2hr and a 4 hr test so that I catch the much slower peak due to low GI and fats carbs. I do see peaks occurring at 4 hr that are larger than the 2 hr readings, and have tracked then to be 6 hrs or so.