It appears that the variations align with school vacations. New Hampshire has Winter Break toward the end of February and Spring Break toward the end of April. Others have a week at Easter which is in early April, and college Spring Break spreads through the 2-4th week of March. They know how many kids are booked and likely expand pool capacity by opening up the solarium - Not fair for those without kids but think about it - maybe 50% of the ship is booked as a family vacation - they may be just giving in to this larger group.