This is more of just a technical question... I am using the API + Reference Transactions to bill customers, but am having trouble deciding WHEN. For example, say I sign up on the 31st of January. When should they be billed in February, since there is no 31st day? My first plan was to just charge them every 30 days, but it would seem most billing systems do in fact bill on "the same day each month", and I just don't happen to have any bills myself that fall in the "problemetic" days. So, should I just charge every 30 days or do the same day every month, or something else? If it is going to be the same day every month, I welcome any suggestions on an algorithm to determine who should be charged. Thanks