They may simply figure that the time of year you are going is quieter and it may not be an issue. And simple fact is, it may not. You could possible be there 4 hours and have a ball or two free the whole time. But the opposite could also happen.

There's no mooring police that will do anything about it, so it really is up to you. You CAN take a ball and remain there the whole time if you want. No one will stop you and odds are no one will even know. I just know its not something I'd do. And personally, I think if no one left aboard would be capable of moving the boat that it is better being in a better spot with that in mind.