I'm not from the deep south, so take my advice for what it costs you. If water isn't an issue then the heat would be the limiting factor and water does mitigate some of the heat issues. The growing degree day thing will be able to closely predict pollination, a good seed salesman will know this number. figure about 50 days I suppose. Then the rest of the time is kernal fill and drydown again roughly fifty days. Doesn't sound like you are harvesting so somewhere around 70 days you will have largly mature ears but maybe doughy inside the kernal.
We get sweet corn up here from Fl. for Memorial Day weekend. It has probably been in the ground 2-2.5 months at that point. The days are cooler so that is what I'm baseing my predictions on. The point being day length has little bearing on corn growing, temperature, fertility,and water have more effect by far.