I‘ve read other people have had the same experience - the
DAS Advance Selections were able to be possibly changed, but all changes had to be made no later than 2 days in advance. In order to make a change, the DAS Advance Selection needed to be cancelled with no guarantee that the day, time or attraction the person wanted would be available.
Once within the 2 day window, the DAS Advance Selections are set and can’t be changed/modified.