From the Model Mayhem FAQ:

How does the recurring payment system work?
Our system automatically processes your subscription payment at the end of the business day when your payment is due. Once your payment information is successfully processed, there is nothing else you need to do.

If your payment information has recently been updated, the system should process the new information at the end of that business day.

If your payment fails for whatever reason, the system will then attempt to process that payment within 7 days. This is a grace period in the event your information is out of date and you need time to get it updated.

If the system is unable to obtain an approval after this 7 day period, your account will automatically be downgraded.