Normally the park doesn't close immediately. I think you can still hop on the Safari ride right up until 5pm. You could take your time and enjoy the scenery- look in some shops, meander through the Oasis... Then when you get to the AKL check in at Boma (let them know you know you are early) and explore the resort until dinner time. You might get lucky and they can seat you earlier.
OR.... if you are park hoppers, stay at AK until 2pm then go somewhere else for a couple of hours then back to the AKL. If you try to do this at 5pm it won't give you much time at your destination before you have to turn back around. Its a lot of transportation and moving but if you don't think you'll be able to kill the time between the park closing and your ADR it might be a good option.
OR... Have you checked to see if they have any earlier ADRs?