Rental cars: fee for late pickup?

I've read in guides for rental cars that sometimes they charge you a fee for showing up too late to pick up your car. However, regarding the azores I read that this is not the case unless you bring back the car outside of business hours. Can someone confirm this? I'm going there in October to visit 3 islands (Sao Miguel, Pico and Faial) and I expect delayed flights or ferries between islands are not uncommon off-season when the weather changes.