You will be asked to stage in a separate area while you wait for all the passengers to disembark. After everyone is off you will be escorted off the ship, go through customs and check in again. Once everyone that is doing a B2B has checked in you will be escorted immediately back on the ship. You will not be allowed to returned to your stateroom because its the crew is busy cleaning all the staterooms and it's chaos. You will be allowed to hang out by the pool while the crew is preparing for the next cruise so I suggest you either wear your pool wear or have it with you.
I have done about a dozen b2b with
DCL and this is not accurate. The only thing consistent on a b2b is that you will get a letter the night before to let you know how it will work for your specific sailing.
But basically, there are two options for leaving the ship. If it is a larger group, they may have you meet in a specific club at a time near when everyone should be off the ship. If you have a meeting place, they will most likely escort you off the ship once they get word that all (or most) other guests have scanned off the ship (we once had to wait an extra 15 minutes while they located a family of 6). If they don't give you a meeting place, they'll instruct you when to head off the ship and what to do to check back in. Basically, you wait until almost everyone else is off, get off and go through customs, then head back up the escalators.
Once they close out the first sailing, the res agents at the desk will check you in for the second sailing (if you were escorted off, this is usually pretty quick; if you walked off yourself, this will depend on how many guests are still left onboard settling their accounts or photos). Once you are checked in, you will have to wait until the ship gives the green light to reboard. This has varied (and has never been immediately after all b2b guests check in). We have waited as little as 15 minutes and have been back on board before they even let new guests into the terminal or as much as 1 1/2 hours when we boarded just a few minutes before concierge of the next sailing. But you are the first to reboard.
When you reboard, you are allowed to go to your stateroom. They don't specifically say anything about cabin access but we (and I think most people) don't go to the staterooms once new passengers start boarding. We either stay out of the cabin and not come back until 1:30 or go to the cabin and stay there until 1:30. We usually stay up on the public decks because we know the stateroom hosts have a lot to do that morning to get ready for new guests and I don't want them to feel that they need to interrupt what they are doing to see that we are okay.
You can hang out in any of the public areas - not just the pool area. There is a lot of activity going on so sometimes it's fun to walk around to see everything that gets done in that short period of time. We have sat by the pools but we have also sat above the atrium. There is usually one place that will be open for you to get coffee and snacks until the new guests start boarding. The drink station will be open. But nothing else that would require a crew member until they open for new guests.
