One nice thing about the 4 night cruise, if they miss CC the first day they still have the last day of the cruise to try again. I hadn't thought of that until our servers pointed that out. Only the 4 day cruise offers the option to try for CC twice, so I would say the odds are better to make it there on a 4 night.
We like having the day at sea after CC on the 4 night, so that is why it is our favorite sailing. We like knowing on the day we are at CC we can just relax and not worry about going back on board to pack or get the kids to the 'farewell' show. But if we had to miss CC on day 3, I am glad we can try again on day 4.
On the 3 night cruise, if they can't make it there is no other chance. This is also true on the 7 night cruises.
DJ