I'm assuming you mean Crystal Palace, right? You could get there as early as you want really. We took the first bus we saw that morning around 6:40am and after dropping people off for Chef Mickey's, we got to the entrance of MK around 7am. There were already people there, some for early ressies and some there just for regular park opening at 9am. When we went there was no one checking names off for ressies. There were two lines to enter through the turnstyles for early ressies. Once you went through there, everyone was in one line by the strollers. A little bit after that they let us into the park (I want to say around 7:45am). Some people went to take pictures, some went to check in at CRT, and some went to check in at CP.
Hope this helps give you at least some idea!