I got B49. It was after coming back from
Castaway Cay and well within the 24 hr checkin period. I do agree that getting early bird is the way to go for the return flight. There were probably at least 10 families in the family boarding group and there were around 6 people behind me. Lol. Getting to the A boarding group is the safest coming from MCO.
We never used the onboard checkin program since our home airport is Midway and have to fly Southwest everytime. Yes, definitely YMMV, I was just surprised to see that some
people have been told no about being checked in.