There are about 4 different roles I believe (I think it was attractions, lifeguarding, concierge, and hospitality) that have to choose role-specific arrival dates. There will be multiple listings on each date. It will say something like "Jan. 7: Attractions only" etc, and there will be one that says "Jan. 7: All roles except attractions, lifeguard, (etc)." In the email with the link to choose dates, it listed which roles needed to choose a separate category and said that if you picked the incorrect category your date may be changed.
So everyone double check if your role is on the list before you set your arrival date! I am in attractions and had to choose an attractions-specific arrival date. For me it was no big deal, there is an attractions category for almost every date. However, some roles like lifeguard, and concierge, don't start until the 2nd or 3rd week. I'm not sure why it is that way, but save yourself the hassle and make sure you pick the correct one!