I doubt you will find a definitive answer from anyone here or even at Hertz. However, I would advise against sending emails all over asking as this will draw attention to any possible loophole to an already generous offer.

If you really want that miles that badly, just rent the car for one day, and return and rent again. Why chance it on the same day rental? Really? Rent from 10:00 and return an hour later and then rent another in 30 minutes? I don't know if you have observed this or not, but an hour rental at Hertz often, if not almost always, equate to a day rate. Why not enjoy the car for the day?

You will have plenty of time to earn all those miles, but what you intend to do is risking paying more money for a not definitive opportunity that you will get those other miles.

Just my thoughts, but do as you wish with your money.