Well, as I said above, it depends.
But the reality has been a mix of course. I'm one of those people who puts in a request for a loop (Preferred level mostly so I request loop 100) and in that I have about five sites (out of 27) that I ask for when I arrive. But if none of those five are available, I will take anything in 100. I've been offered a site in 200 (also Preferred) but chose to wait for anything in 100.
My worst experience was one of my five requested sites in 100 that had a guest on it who was scheduled to leave on my arrival day. I got it swapped over to to me and waited for the text by 11am indicating the guest had left and the site had been clean and prepped. It never came. I bussed down to 100 to look at the site. RV still on it and making no preparations to leave. So I called the Fort front desk. And they phoned the guest on their cell phone. And the guest decided to extend their stay and remain on the site a few more days (there were available Preferred sites for the next several nights). So I had to take what I could get (only 200 remained available by that time) and then moved to 100 loop the next day after one night in 200.
Once or twice I've been able to roll right down and set up immediately in 100 (first available in 100) but that's rare because that generally means a site sat empty overnight which is rare in 100 since it's in high demand. Usually, though, by 10am I can get my site for all the reasons outlined above (like getting my request for a site in with the CM before most of the texts have gone out to that day's arrivals).
So it generally works for me but every experience is different. YMMV. Besides, my arrival day never has a park planned - I use it to set up and enjoy the ambiance of the Fort. If you don't care about what loop and/or what site, your general wait will be null or shorter. For folks like me who do care, I'm willing to wait more.
Whatever.
Bama Ed