Hi , I am from the UK and visited end of March and August this year.
March was busier as the last weekend of the month was Easter and generally the parks were crowded.
From the middle of August it is not too bad at all crowd wise and most of the schools have returned by then, it is a good time to visit.
The only downside to August is the weather is much hotter with high humidity and more frequent thunderstorms also.
The parks do tend to shut earlier as you go through August, although there are still some later nights, especially at weekends.