Its hard to say. I would worry as much about the price as availability, as admission costs tend to increase the closer you get to your visit day.
We are also going in August (the last week of the month), and we booked our tickets in October. Even since then, with many months still to go before our vacation, prices have already increased for two days during that week by $30 per person from what we paid.
If you can be flexible on the day of the week, you'll probably be okay one month ahead in booking at least something. There may be a day (or days) that are sold out, its difficult to know.
The dolphin swim is so much fun. You'll love it.