My children and I were staying in the hotel June 7 - June 10, and the hotel guests pretty much had the place to themselves for the first couple of hours although they were letting a handful (I presumed) of non-hotel guests in an hour or two before closing the Wizarding World around noon each day.
Here's what the Butterbeer line looked like during our stay:
And here's what it looked like on opening day a week later:
A friend of mine went later that summer and said it took her two hours to purchase a chocolate frog. Not a problem if you live in Florida, but a bit of an issue if you're paying for plane tickets from Texas, hotel rooms, and tickets for 3 or 4. If I bought onsite hotel/Diagon Alley tickets again, I would definitely expect either everything to be up and running 100% so I could at least enjoy it all during my first pre-opening hour each morning, or to have mostly exclusive access to the park for a few hours if everything weren't up and running all day.