Your payment method is billed when your character transfer is completed. When the transfer is actually begun, be it at a scheduled downtime, or on-the-fly when mod 5 goes live.
We sympathize with your desire to not lose any time with your character while you are also paying for your account, however, you would not want the move to be done in a shoddy manner. Due to current technology restraints, we feel it is best for the entire population if transfers occur during maintenance periods.
Moving a character is not taken lightly. So as to avoid data-corruption and other unfortunate events, this safety precaution was made to insure an event-free transfer.
We, more than anyone, want to see you having fun with the game.
We make every effort to expedite the process, and thank you for your patience.