Some...

"Your Amazon EC2 usage is calculated by either the hour or the second based on the size of the instance, operating system, and the AWS Region where the instances are launched" - https://repost.aws/knowledge-center/ec2-instance-hour-billin...

https://aws.amazon.com/ec2/pricing/on-demand/

MacOS instances appear to be the sole remaining exception since RHEL got on board.