We've hit on this topic before, but I think it bears repeating. I read a story on-line today of a group that showed up at the pier at 4:30pm in Long Beach - yes 4:30pm - with the ship sailing within an hour. They were denied boarding. This is because of federal requirements for a final manifest to be submitted no later than 60 minutes prior to scheduled departure time. Of course, in their complaint it is all Royal Caribbean's fault and everyone was mean to them.
The gripe didn't state whether these people had completed online check-in, but if you don't then you are required to be checked-in 90 minutes prior to scheduled departure.
Either way, it was the passenger's fault for missing the ship. Don't let ignorance of the rules be your excuse. Get to the ship as early as possible.
Frankly showing up at 4:30pm (and they apparently had no delays) is just plain stupid.