As commented above, extra hour doesn't exist in Europe.
But the question has its interest. Indeed I booked on spanish website for a renting in France. The email I received for the confirmation includes a very parsed information about the contract. But it clearly precises ONE EXTRA DAY for delay (Delay period is not precised since it may vary from one office to another, but in this particular case it was 29 mn period). It is also proposed to visit a URL to know more about general conditions of sales. I tried and nothing interesting came out.

As I don't know the complete contract and I don't know what would have be written if I had booked on the French website I called once again customer hotline.
The agent helped me to find more information about full detail of contract. In vain. Then asked me details of my renting. Look 20 sec, checked my booking code and fare. He said, well yes in France an extra day after 4 days is a full week. But on your confirmation it is precised that extra day is 11,50 euros + VAT. He added that there was a mistake in the answer they gave me and certainly didn't read properly my booking information which is half in spanish half in english. If they would, they would have read clearly that they couldn't charged me full week, especially at the rate or the fare they did.

Conclusion : I got canceled the 394 euros extra and got my extra day at 11,50 euros + VAT + some other extras stuff that I don't understand but making a total of 207 euros instead of 563 euros ... saving me 356 euros.

GREEEEEEEAT!!! I don't know if we call this luck or not. Thanks for your posts, all this litterature I wrote to answer you, helped me a lot to structure my thoughts and my arguments towards Hertz. Truly many thanks.

Cheers,
Jer.