I assume your B2B is out of PC. Several years ago we did a B2B with Barcelona as home base. We are doing another one next fall with Dover UK as the turn around point. For the first one, we planned a day's activity to fill the time, since Barcelona has so much to see, during that switch-over day. This worked out great for us. We had the same stateroom for both cruises, so no moving of luggage. As stated before, you will get a letter the night before with all the details. But, you don't have to get back on the ship right away if you don't want to. In Dover,
DCL has an excursion to see the old fort that overlooks the port and a short drive to the town of Sandwich (yumm!). We hope to see more of the UK since we live so far away (West Coast). All this assumes that things will be close to the old normal...we can only hope.