I also have a 500 gallon tank for our house, and we are renting the tank from the propane co., so we are on a auto fill. In the winter months, they come out about every 40 days or so and top us off and in the summer it is several months.
Now, at my business, our fork lift tanks can only be swapped out on a Weds, since that is when they are in the area. So we have two tanks. When one runs out, we call to schedule then to swap us out on the next Weds they are in the area. So it could be 7 days or it could be 1 day, all depends on what day we call.
So it could be that you called after they have already been in your area, and will be back in your area in week. So to answer your question, yes it is a little long, but no if you missed them being in your area.
I know that I am going to have to watch the 500 gallon tank on my garage, since I purchased the tank and I am not on a auto fill, then I will have to call it in, then I would be able to give you a better answer when that time comes.