Enjoy your 1st trip!!! If you can, I would show up at the park about 15 minutes before it opens. There will be a line to enter for character breakfasts and you should be able to go right in and head back to CP. Have your ADR confirmation number with you in case they ask for it.
The reason I say this is last December we had a 9:30 ADR at Tusker House in AK and rode the bus with a family that had a 9:20 ADR. We got to the lines to enter the park about 8:55 a.m. AK had just shut down the character breakfast entry line to prepare for the rope drop ceremony, so the other family was told they had to get at the back of the long lines at the gates to enter the park. Then once the gates opened, not only did they have to wait in the line, but we all then hit a traffic jam and got blocked by the rope drop ceremony. We all got to the restaurant right around 9:30. The good news is that even though they were a few minutes late, they did not have any problems. CP shouldn't take as long to walk to from the front gates as Tusker House, but it still would be good to be early rather than late. Plus, I don't know if this will be your 1st day in the MK, but a nice leisurely stroll down Main Street to take it all in as you start off, rather than a run to get to a restaurant in time, would sure be nice.