You should be same as NC. Here, I wait as late as I can to plant, as I want to make sure deer, bear, coons and other grain eaters don't get it all before the ducks get a chance. Latest I usually plant impoundments is around June 1st. Different corn varieties have different maturity days, generally between 90 and 110 days. Also, different varieties have the ears at different heights on the stalk. I prefer the low ear, short maturity combination for flooded impoundments. Down East, we have a terrible problem with the Tundra Swan that will, and do, plop into impoundments and literally eat all the corn before the ducks even get a chance. We have resorted to putting up hog wire fences around the crop in the impoundment to keep the swan out.
Millet is generally in the 90 day maturity range with Jap millet being a few days shorter so you can plant later.
Your rice varieties range generally from 110 to 150 days, germination to maturity. So you must plant it earlier. I have better success with rice if, after it reaches about 6 inches in height, I flood the impoundment to about 4 inches. This keeps the weeds out. Some impoundments I am able to flood the rice and leave the corn dry (planting the rice in the lower elevations of the impoundment) I have several hoe drains running thru the corn rows to the low part, thru which I run my water, which helps irrigate the corn.
Secret to most successful duck ponds is the ability to control the water.