You wont be out of luck. But I do suggest thinking about those few things that might be easier to do w/out the 2 year old that you might want to do and prebook a few slots before the cruise. A few hours here are there are always nice. Maybe for dinner, some 1:1 time with the older child, or even a couple of hours by the adult pool are always a plus. Kids are

wonderful, but a little break while on vacation is always a nice treat (even at $6 an hour)
I had not heard about any new open hours policy, but you do now have me curious. on the past sailings we have been on, Open House, was those first few hours that you got on the ship (before it left port), for parents and kids to come in and check out the kids club/lab together and meet some of the counselors. Same with the Nursery. After that the Nursery did not allow parents in, you had to drop off at the door. With the Oceanears lab, parents were welcome to bring in the younger child (under 3) for supervised play (but parents had to stay). I am interested to hear what their new policies are.