Monday was a haliday here in germany so all rental places (beside the airport) where closed.
I rented a car for the weekend and returned it Monday night.
The only problem would be (I took the risk) that if the parking lot is full (Avis) I had to park the car in the Parkhouse next door and that might have been a problem, but Thanks G-D everything worked out well (I found a small spot and squeeze in the car) !
Germany is not America though

never would they officially let me return the car later (I asked once so they told me I have to call the company i f I come late

)