When cruising on Voyager from Miami, we were at the pier at 10.30, boarding startet at 11.00, we were onboard by 11.15. It was about the same with Enchantment from Fort Lauderdale.
Make sure you have filled in the online form. Print it out and bring it along, with this you should be put in the line which gets to check in first. Worked for us both in Miami and Fort Lauderdale...
Marc