Depending on each publisher, your credit card will be charged each week (7 days after the start of your campaign or when a certain amount is reached), based on the impressions delivered.
This amount varies from a publisher to publisher, but on average the most used amount is $100.
Your final invoice can take from 48 to 72 hours to be produced after a campaign has ended. This is primarily due to the final confirmation step, which ensures that you are only billed for the impressions that were delivered.