You will be billed upon signing up for the first month of coverage. The following payments will be deducted on the first day of the second month of coverage and continue on that day every month. For example, if you signed up on the 14th of September with a start date of the 1st of October, then your next billing date will be on the 1st of November, and so on.
If you would like to learn more about expat health insurance or would like to sign up, you can do so here.