We offer multiple "scaling modes" for both CPU and Memory, which determine how aggressively your server scales up and down. Resources are invoiced based on the scaling mode that you select. A more "aggressive" scaling mode, which adapts quicker to changes, will cost relatively more because it will assign more resources than a less aggressive scaling mode.
The default scaling mode is called "Standard Performance". In that scaling mode, you can exceed your invoiced resources for one hour before being billed for the next resource. For example, if you're paying for 1 CPU core, you can use 2 CPU cores for 45 minutes without increasing your bill. If you use 2 CPU cores for one hour, you will be invoiced for 2 total CPU cores.