Those are not in fact limits:

> There can be a delay between when you incur a charge and when you receive a notification from AWS Budgets for the charge. This is due to a delay between when an AWS resource is used and when that resource usage is billed. You might incur additional costs or usage that exceed your budget notification threshold before AWS Budgets can notify you, and your actual costs or usage may continue to increase or decrease after you receive the notification.