There is a delay. But it is not 10 seconds and I have not seen any AWS documentation that says as much. From personal experience having Lambdas inside a VPC, called by API Gateway then communicating with an RDS database I think the worst delay I saw was 1.5 seconds. This isn’t reading from a blog post but having it actually running. Without a VPC its < 1 second so there is a difference but it is not 10 seconds.