macmom.. I have gotten these also. Nobody (or at least very few) people seem to pay attention since there is still a mob scene around noon. They are just trying to level out the flow of passengers. My theory is they send this note out to probably half the passenger list hoping to push some of the arrivals to later in the embarkation day.
I tend to ignore them. Being a platinum cruiser has its advantages, one being not to have to deal with the long lines and limited seating area during peak arrival time. But you can do as you see fit.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007