Car Rental after hours returns are those in which you return the rental car after the location is closed.
More and more, rental companies are restricting this practice.
For small neighborhood locations there are liablity issues. Because they can't inspect the rental car when it's returned, the rental car location must assume that any damage to the vehicle is the responsibility of the renter.
It's almost impossible to prove that when you dropped off the rental car, it was fine! (Unless you take photographs of the vehicle with a camera that is date/time stamped that can't be manipulated.)
Even if a car rental location does not generally offer late drop off, you may be able to work out an arrangement.
Your best bet is to call the location and ask to speak to the manager. They may be able to work out something with you, that will allow you to return the rental car after the location has closed.
Make sure that you have a clear understanding of what the rental company determines will be the drop off time. If the car rental company will not officially check in the car until they open in the morning, then your after hours return could cost you an extra daily charge anyway.
Most airport car rental locations that are not open 24 hours will still allow late drop offs after the counter closes. There is a lot of security on the grounds of the airports and in the parking garages. Each location will determine the availibility of this option. Check with the company directly for restrictions and instructions on how and where to drop off the car.