As seems to be the case with Carnival, there is some lack of consistancy from ship to ship on this.
I have read that some people actually go to the Purser's Desk and request that someone walk them to the head of the line.
We have never done this. We have simply used our Platinum card as our pass. This prevented us from having to go to the theater and getting "a number".
We have always just used our Platinum card as a number one ticket (without having to go get one).
On the Imagination, (this was a first for us)..they asked everyone to come to the main theater and all Platinum guests were escorted out of the theater first (even before Carnival excursion people).
But normally we just get in line whenever we decide to leave...we just don't have to go get a ticket to do it.
In Belize hubby and oldest son had a 9:15am excursion which required them to be the first ones off the ship. They simply walked down to the debarkation location early and was on the first tender in. Again, no number needed...they just flashed the Platinum card.