I'm in SW Texas at 4500 ft elevation. Last year I had ripe corn continuously from mid June until November. I did this by planting every two weeks from March until early August. So in zone 8 you could probably plant until mid-late August if your corn is 75-90 day maturity.

Your only problem planting now is the excessive heat and dryness. With lots of irrigation and nitrogen, you could make a crop planting now. It might be easier to make a crop planting say late July because it will be cooler at tasseling and pollination. I'd recommend a 90 day corn like Silver Queen. The short days of fall will make the plants smaller so you want a plant with some size. Allow sufficient time before frost. If it frosts before maturity the crop may be lost.

Thought I'd give a little more detail on how to time successive plantings of sweetcorn. I plant my first planting as early as possible with about a 66 day corn. About 7-10 days later I plant a 76 day corn. From then on plant the next planting of 76 day corn when the previous planting is 4-6 inches tall. This will give continuous corn all summer. If you want a one week break between plantings, plant each time the previous planting reaches 12 inches.