There seems to be a trend lately that they only release earlier dining times at the 90 day mark, then a month or so later, they open up the later dining times.
On our 90 day mark, concierge made dinner reservations for us at CRT. I had requested 7pm but they were only able to get 5:45pm, as the latest. I kept that reservation but about a month out I called CRO myself and was able to change it to 7:05pm.
To answer your question more specifically, I don't think you will need to get up at 7am on the 90 day mark to make dinner reservations for CRT, unless you will be there during a busy time, such as holidays. If it were me though, I'd call on that day, but at your leisure, not at 7am. lol If the times they offer you are too early in the evening, just take the best you can get (just in case!), then call back a month or so later and try for the exact time you want.
I hope this helps!!

I love dinner in the castle!
P.S. I had to do the same thing with dinner at 50's Prime Time at MGM; concierge was only able to get an earlier dining time, but a month or so later, I called back and the later dining times had opened up, so I changed it.