If took a car out at 6pm, and don't return until 8pm, you will be charged an extra day. Hertz give you 30 minutes grace, and after that, an extra day is payable. The Rental Agreement is very explicit about this, so you won't be able to try any "hard luck" stories.

Good luck in trying to get a Golf sized Automatic for a good price - Hertz tend to have relatively few small cars with an auto gearbox in Europe, and as you want to drop it off in another country, you are compounding the difficulty in getting a favourable rate. Sorry!