We're Platinum and the first available boarding time was noon when we checked in. For those who don't know, one of the benefits is checking in 2 days prior to the normal check in.
Also we received the following in an email:
"Dear Diamond & Platinum Guests,
You may have heard that Carnival Jubilee’s naming ceremony will be taking place Saturday, February 24.
To ensure a smooth experience for our guests and manage all the activities, Terminal Arrival Appointments will begin at noon. Please DO NOT arrive prior to your Terminal Arrival Appointments as they will be STRICTLY ENFORCED and all guests who arrive outside their designated times will be asked to return.
Although the ceremony itself will be an invitation-only affair, we are delighted to share that it will be televised on big screens around the vessel, starting at 3:30 PM. "