Just keep in mind that SUNDAYs is when folks start leaving the camp ground - some leave early some leave in the afternoon... Your reservation site might not be ready until the late afternoon. You might check with the campground and see if your site is available for Saturday as well. They might let you in on SAT if no one is there?
Most high-end camp grounds have a overflow area to accommodate early arrival campers...
Sunday is always a good day for us checking-in as most campgrounds are completely empty on Sundays...
Roy Ken
