Help CenterWhen you start doing ads, they can have limits on you initally and it rises based on if you hit their limits and your card is charged.
If limits do not come into play, generally you will be notified on the last day of the month, to about the 2nd of the month of being charged. Your card will be charged on around the 2nd of the month, on any outstanding balance. You can get your bill even after being charged. You can view what your charges will be by using date range on your ads, or picking current month before it goes to the next month (if it has, you can look at last months totals as well to give you an idea).
Please see this article from Amazon Ads, for a full understanding of their billing process, Advertising Billing, Understanding Your Invoice & Understand Amazon Ads Charges and Invoicing. Yes they have a lot of articles!