You'll want to call and ask that....a possible problem would be if there are no later reservations available.
If that doesn't work, you might want to stop by the podium early in the day and ask. The first time we went to CRT we had done GF Tea earlier in the day and were still full....so I called to try to move it up and was told no availability......so since it was prepaid we went to check in and explained asking if we could delay it and they didn't even bat an eye asking ME what time I wanted to come back. I wasn't upset by this, I kinda figured the phone folks can only go by what they see on the computer screen...whereas those working it know how much flexibility they have.
So, it definitely is worth stopping by and asking......