It was super easy, we did it in August. We were asked to meet in the cinema after breakfast, we sat in there for 20-30 minutes. We were escorted back into the departure lounge. We were there about 40 minutes and just walked back on board.
You don't get announced the second time, but the ship is as empty as you will ever see it during the day! Perfect time to get some photos. Cove Cafe was open (and my son came in with me as he's 10 and I was not travelling with anyone else) for drinks and I think they had the usual snacks. You need to wait until everywhere else opens to get food. Pool was empty, I don't remember if the Aquaduck was running but you should be able to get in line first if that's what you want to try!
I think the best thing for us was that we didn't feel like we needed to go to the dining room the second cruise (3 nights, the first was 4 nights). So we had more time in the evening, we saw Aladdin on the first cruise and Frozen on the second. If there was stuff we missed we then did it on the second cruise.
We changed rooms and we got robes on the second cruise! I wasn't expecting this!
I hope you have a great time!