I return cars to Hertz after hours all the time. My first rule of renting a car is time stamped photos all around the car at pickup and at drop off.

I did have one issue with this at Hertz, I had dropped off a car after hours to a Hertz that was in a shopping mall with a couple of bars in it as well. The next day (Saturday) I noticed that I hadn't received a receipt yet, so I called and asked what was going on. He said the passenger side window was smashed and they were working out the damage report and had planned to call me that afternoon to ask me about it. I provided time stamped photos of it's condition on drop off and that cleared it up immediately.

I'm not sure if Hertz has the same provision, probably do, but it is best in this situations to cover yourself as best you can.