I thought I'd answer my own question.
I received an email from RCCL the week before we sailed offering the My Time Dining to us. They directed us to our travel agent to make the request and to pay the gratuities. If you don't make the arrangements ahead of time for MTD you should go to Guest Relations to request the change as soon as you board the ship.
We sailed on Serenade of the Seas the week of March 15 and used My Time Dining. It worked out wonderfully for our family. We did have to prepay our gratuities for the stateroom attendant, head waiter, waiter and asst. waiter, but they were all so wonderful to us that we tipped them more at the end of the cruise.
We made standing reservations for a certain table by the window with the same waite staff every night. When they saw us coming they had our bottles of wine delivered and the kids had their sodas without even asking for them. We ate late enough to enjoy the sail away parties and still have time to freshen up and early enough to enjoy the second show at the theater.
RCCL had devoted a little less than one-half of the 5th floor of the Reflections Dining Room for MTD. The remainder of the floor plus 4th floor Reflections were all early/late seatings. The waiters liked the MTD as it made their evenings more interesting instead of doing the same thing all at the same time -- monotonous as one said.
My Time Dining may not be for everyone, but it certainly worked out well for my family.