"Idle Termination Time" has the following usage of negative value:

"If a node has an idle timeout of -5, and it becomes idle at 11:58, it will be terminated because it's within 5 minutes of the end of the billing period - even if it was active less than 5 minutes ago."

I propose to separate the "negative value" functionality into a separate parameter "EC2 Hourly Cutoff" which could be used in combo with "Idle Termination Time".

For example, I would like to terminate instances 5 mins before the end of the hour IF they've been idle for at least 10 minutes, otherwise keep them alive. This way I can keep workers alive the maximum amount of time possible with minimal billing.