One slight modification to what vegasguys said. You actually can return the car after hours. There is a drop box for the keys, and they will mail you the receipt.
The hotel desks are a little more laid back, as there is often only one person working. Usually, if you don't have any damage to declare, they just process your paperwork and someone inspects the vehicle later.
I guess you could ask if the person can do it right then. But if you know there is no damage, I also wouldn't lose a lot of sleep over it. Hertz is a reputable company, and I've never had a problem with them accusing me of damaging a vehicle.
Also know, you can pick up at the hotel and drop off at the airport (rental car center), and Hertz does not charge an additional fee for this.
In fact, for my two upcoming reservations, I am saving big money by doing this, as the daily airport fee does not apply if you rent at the hotel.