Saying there are 30 iterations planned is interesting, too. The more there are, the less certain they are for sure. You can solidly plan one or two and tentatively plan the next couple but I'd guess it's usually not much worth doing any detail on the rest. Saying that there are 30 (or any number) is betting that your velocity will hold true to some expectation. If one iteration comes in under the expectation it might be an isolated technical problem or one poor estimate. If a few in a row come in under expectation, it's time to adjust the scope or the number of iterations.
BTW: You can surely go for too few iterations, too. We had a couple releases scheduled for two iterations, way too short for our imperfect
test & feedback loop!