Sounds like a great first day so far, though your hints for the upcoming posts are kind of daunting! lol hope that it worked out to be a fun time and your room wasn't lost for too long.
With the check in times, this is my guess: They give you a check in time, but if you are early, they will let you in early. If there is a huge influx of guests at an earlier time, they will probably check in the guests who are "supposed" to be there early first, but if it's not busy, then they won't make you sit there and wait for hours. They probably give different check in times as a means of crowd control.
Now, that is just a guess! I've never cruised on
DCL before. I can't believe the CM was rude during the muster drill, what a lousy attitude to start out a vacation with, but glad that it seemed like his supervisors were handling him. Hopefully he didn't negatively impact anyone's cruise!