I booked a 2 bedroom and a studio in the Value category at Jambo for mid-August of this year. (Then I ended up cancelling both, when we changed our travel plans.)
I did this by stalking the reservation system, at the edge of the 11 month window, and walking. Stalking the reservation system, to me, is when you sign on at 8 AM Eastern time, and run 'dry runs' for multiple mornings over a period of time. Think of it as walking your 'hunting' grounds and getting the 'lay of the land' before you actually start the hunt. You do this to get a good sense of what is happening with the rooms/units you want, to give you an idea of when you need to start Walking.
To get the 2 rooms, I started almost 2 weeks in advance (it wasn't the busiest time of the year) and I needed to get a Studio, and a 2 bedroom Lock Off. It didn't matter which one I got first, since I needed, in essence, two Studios. By that I mean that I needed a Value Studio AND then a 2nd Value Studio + a 1-bedroom, to make the 2 Bedroom Lock off. Clearly, I was only going to be able to do this in one morning IF there were at least several Value Studios hanging around for a number of minutes, so I would have time to get both, but there weren't. I was ready to go, right at 8 AM, and clicking my mouse the instant the clock rolled over from 7:59 to 8:00. Even doing it as instantaneously as I could, I got nothing for the first few days. On the 3rd day I got the 2-Bedroom and on the 4th day I got the other Studio. And then I walked them to the days I needed.
It wasn't easy. If you check things out this way, you will find that ON MOST DAYS there is no availability at all, because there are a very limited number of rooms and people are walking them. The time you mentioned is also not THE MOST BUSY TIME, but it is still plenty busy. You might need to start even earlier, and be willing to walk for several weeks.