I used miles to book HNL-LIH-HNL last year and it was a major pain. I had to find partner award availability on EF and then call Delta a few times until I found an agent that knew how to push it through. There is a thread about it on here somewhere. As far as dropping a car off when they aren't open, I dropped off my car at National and noted the time and mileage and it wasn't an issue.