Just for grins BJ
I must tell you Midnight is the Zero hour, in other words the beginning, not the end of the day. What you have said is a contradiction.
But it is a wonderful example of how popular misconceptions create issues where there really aren't any, well almost none, assumption should always be suspect and circles aren't the exact same thing as cycles.
The last minute of the day is officially 23:59, or 11:59 pm. In other words any submission ON Sept 7th will be accepted by the rule you are trying to provide. By the way it is from this fact of time that we get the expression; "The eleventh hour", which is used in a variety of linguistic manners to describe the last minute.
In the future when you describe the entry rules for an event, if you say for example "through Sept. 7th" instead of "by Sept 7th" there would be less ambiguity. But I think most of us get it anyway.