I think some of this is because most of us are “trained” by the school system to start things in last August/early September and in January, since that’s when school usually starts and we get past the summer or winter break periods.
I started studying for the December 2014 exam in September. I think the reason there is no correlation with the amount of time someone had to study and how well they do is because its a matter of ambition. And financial industry is very competitive and ambitious as it is. 😉