The 7-day payout window covers the first 168 hours after the post is published. The moment the first minute after those 168 hours is reached the post is technically evergreen content. Evergreen content is any older content which has value because it doesn't rely on time; tutorials and guides fit this description, so they are always in demand.
Evergreen content drives search engine traffic back to the domain where it was published, so it has value to Hive as a whole if not directly to the original Hiver. This is also why it makes a difference which front-end is used to publish the post.
Evergreen is a great way of describing it. The comments and content are always there, blooming for all to see and interact with. Great point!