To add to this thread, if you begin your rental early, they now also adjust the dropoff time to match what time you either selected the car or got the papers/left the lot.

I got a notification when selecting a car last week (LGA) that if i started early and returned at the originally scheduled time, i may incur extra time charges. I returned it earlier than scheduled anyway so I didnt have to worry but just FYI for anyone else reading this.