It will also depend on what way your zbS is heading when you eat, whether you have any fast acting insulin on board from earlier, and if your basal is correct.
If you had the bread as a snack or meal and bolused for it, then I'd keep testing at maybe half hour intervals if you're interested in how your BS reacts.
I eat bread and jam and stay below 7, but I bolus in advance.
I'm not quite sure what you're trying to,discover. If you're concerned about your digestion, then it's probably best to speak to your DSN.