Since it appears that none of the other guys answered your question about “billing cycle”, I will.
Despite having paid for a year of service, DH runs a monthly billing cycle. Seems strange until you realize that that same cycle is the one that causes your usage to reset each month. So, the trick is that the billing cycle is just used to calculate your usage limits and to ensure that anything you do that creates extra charges (registrations, overages, unique IP) are billed at that time.
Wholly - Use promo code WhollyMindless for full 97$ credit. Let me know if you want something else!