We booked nursery time around our Couples Choice massage and our Palo dinner when we went on the Dream in Nov. We are going on a Wonder MR in a few weeks and we booked time again for the Couples Choice and Palo, but this time we also added a few hours on a sea day to check out the adult pool area and a few hours after dinner one night to check out the adult clubs.
In my opinion, I would book the hours they give you online so you have them. If you decide not to use them, you can always cancel while on board. We had nursery time booked for an hour the first night and we all were too tired so we cancelled and they were great about it.