You can register any time you would like. You can always withdraw from the match, anytime up until ROL lists are due, for prematches. If you were to actually get a prematch prior to Nov 30th, you would lose your NRMP match fee (which you don't get back if you withdraw, I believe).
If you register after Nov 30th, it just costs you an additional $50. I believe you can register for the match anytime up until ROL lists are due in February. The match fee is $40, which is small potatoes compared with all th eother costs associated with applying for a residency. Long rank lists make the match much more expensive.
