Regardless of which payment method you choose, you will not be charged for a continuing subscription before your free game time has expired. If you have any questions about the process, please read the FAQ.
Bioware cites the play time tied to the purchase of the game as being "free". Seems that is not the case. Unless they redefined the meaning of "free" while I was not looking. And do you lose 1-5 days of the "free" time between game registration and complying with the strings attached?