I also have a car reserved during Christmas week using the ENTERTAIN code. Other posters previously reported no problem using it after the code was no longer valid.
LvsTnk, if you can get access to a computer after picking up your rental I'd appreciate it if you could post whether you have any problems. I arrive on 12/22 and hope everything goes smoothly.
Just take a copy of your reservation with you, you shouldn't have any problem. Dollar is very good with honoring their reservations no matter when they were made. I don't think you will have a problem. Calling them may put your mind at ease. Just ask them to comfirm your reservation, nothing more. I won't even mention the code, just confirm date and price. Enjoy!