Thanks for your question, and I'm glad to see that our tool may be of use to you. One of the options on our tool is actually optimized specifically for corn (the 86/50 threshold). Corn does not grow and develop above 50 degrees Fahrenheit, so this is set as the base temperature, and it also does not perform well about 86 degrees Fahrenheit, so this is the maximum temperature.
As far as developmental milestones go, depending on your corn variety, it is generally ready to harvest after it has accumulated approximately 2500 growing degree days.
Thanks and post again with any other questions!