We are Platinum and sailed on the Magic 12/23. It was so easy.
We arrived about 11am there was no line to enter the terminal and a very short line to go through security. Both took about 5 minutes.
The check in desk for Platinum is at the back of the terminal so you don't have to walk through everyone.
Check in took just a few minutes we were given boarding #1. They were about to announce the Family of the Day.
I had read on these boards that they allowed Platinum to board through the concierge. I had to ask and they allowed us. We boarded right away. We were on before 11:30.