I always go to the desk on day 1 or 2 of the cruise (we have only done 7-day cruises), and I get to the cruise desk about 5 - 10 minutes before she opens, so I'm first in line. This last cruise we did (1/30 eastern Magic sailing), I waited for 5 minutes before her desk opened (as soon as she arrived to her desk before she "opened" I just went up to her to let her know I'm waiting for her, so that way if someone else came up right when she opened, she would know I was there first), and I was the first person she was able to help after she opened, and I was done in less than 5 minutes.
And, I was glad I told her I was waiting when she was opening, because sure enough, as soon as she sat down at her desk and was officially opened, another person just went and sat down at her desk not realizing I had been waiting, and the
travel agent very nicely told that person that I had been there first. The person was totally understanding, so there was no issue at all, but if i had not told her I had been waiting, she might have helped that other person first.
I think the trick is to book on day 1 or 2 of the cruise, and figure out her desk hours, and just get there before her desk opens and wait.... I did notice by day 5, 6, and even the morning we docked at Port Canaveral there were a lot of people in line all day long when her desk was open.