They do let guest in early, yes. Keep an eye out for the special line/sign at park opening. I had some trouble finding it LOL. It was a little confusing for me. But yes, anytime, at any of the parks where they have a breakfast reservation before park opening, you get to go in early, though, of course, only get to go directly to your reservation, you can't go on rides or anything, in fact it's roped off to make sure you don't go where you're supposed to at Magic Kingdom, in fact. I remember on the line for this to get in early, the person actually had a list of people so when I gave him my name for my Be Our Guest reservation, he could check it to make sure I actually had one before he let me through.