Hi,
We usually get to the disney park for emh every morning, we find it's a good opprotunity for the kids to do rides like Peter Pan, dunbo, buzz etc over and over as these get quite busy during main park opening hour. Also if your there for just as it's open we have found that we are the only ones walking down main street which is great for taking some lovely pictures of main street and the castle with no one in them.
We then a few days head for Studio's for 9.15 for the 9.30 opening (as Ware Bears have said) to try and get to Crush before that gets busy (I have been there when they have opened crush at 9.30 instead of the usual 10am and got 2 goes in a row) and the other days stay in the park and wait for rope drops for Pirates or Btm. HTH