I don't know specifically the answers but here are my thoughts since no one else has responded.
Pizza: I would think probably pretty quickly. Actually I think any foods will change blood glucose levels fairly quickly. The measure of this is the glycemic index and the glycemic load. (Load involves the combination of the GI and a suggested serving size.) Here is what kind of complicates things. A white crust pizza is made from refined flours and is probably roughly equivalent to any white bread. But if you load it up with full fat, cheese, pepperoni and sausage for example, all of that added fat and protein will slow the absorption of the carbohydrates into your system and effectively lower the GI of the entire entity called "pizza". The problem of course is that doesn't make it healthier, just lower glycemically on how quickly it affects your blood sugars. In that example you are still getting a whopping amount of saturated fats and sodium and not doing your health any favors at all.
Exercise: Again, I am no exercise physiologist, but I would think it would lower them as you are creating greater demand on your muscles and body for energy and blood glucose is the fuel your body (and brain!) works with. Since endurance athletes generally need to ingest relatively ready-to-use carbs along the way to keep from "bonking" on extended training sessions, I am guessing that their blood sugars have been decreasing all along, their glycogen stores have been depleted and the conversion of fat to energy doesn't occur fast enough at that point to help out much, so the choices are eat something high GI that converts to blood glucose very quickly or "bonk" and run out of energy to continue their exercise session. That's not something most of us have to deal with however!
For info on the glycemic index I would go to http://www.glycemicindex.com/
which comes from the people at the Univ. of Sydney who pioneered the concepts. And while it doesn't really answer the questions about blood glucose and exercise, this article at the Harvard School of Public Health helps with understanding the myriad of benefits of regular exercise! http://www.hsph.harvard.edu/nutritionso ... index.html
You might just need to google around on your own for more specific info on that topic.
it's kind of an expensive option, but you could buy some kind of a blood glucose monitor or get a diabetic type kit that can measure blood glucose with finger pricks and do your own research on yourself!!