Dont forget, once you get your permit, you still have to schedule your exam days with prometric. The longer you wait, the less likely you will get the days you want. In the example previously cited, if you knew that you were going to schedule your test in May, I would apply in the beginning of March, that way, the whole month of May will be in your 90 day window, but you will get the jump on other applicants to schedule the days that you want