Well, it depends on the information you want to get. When I first started using insulin, I wanted to know when my peak was, and how high it was, so I tested 1/2 hr, 1 hr, 1 1/2 hrs. and 2 hours to find out when MY peak was. It turned out to be 1 1/2 hrs, so the 2 hr. advice would not have served me well. Knowing how high I peak is important to me, because it teaches me what foods to avoid, and how much to limit portions and carbs in order to keep the peaks as low as possible.
But when you want to know when to correct, it depends on how long the insulin lasts for you. It gets out of the system faster for some people than others. The way I figured it out was with my CGM – after 1 1/2 hrs. the peak starts coming down, but at 3 hours, it levels off, even if it hasn’t gotten down as low as I want it to. So I figure insulin lasts 3 hours for me. So between 3 and 4 hours, I can test and correct if need be. But you could figure that out with your meter and strips, too, if you have enough. Keep testing every half hour, and see what your BG does. But do remember that high fat+carb (like pizza) meals keep on raising your BG for a lot longer than a low-carb, high fat and protein meals does. So you have to have a couple of different action plans depending on the composition of the meal. I haven’t got the pizza part down yet, because I square bolused for it tonight, and ended up going low. Gonna try plan Q (when plans A, B, C, etc. don’t work!) next time!