there's really no optimal time, aside from the following extremely general criteria:
* you have to sit for the exam within 5 years of your application date (which isn't a problem with the application date you've suggested);
* you have to sit for the exam before the deadline date set by whatever schools you're applying to.

apart from those criteria - which certainly won't pose problems for you - there's no reason to choose any particular date over another, except for reasons pertaining to your own personal preparation.
in other words:
take it when you're ready - but only when you're ready.