Hopefully they're taking into account the actual active times of the fans of a page. If your fans are fairly local, which would map a lot of sense for a newspaper, a page could have huge swings in engagement throughout the day on the same content.
If they're smart they have a model of how they expect a post to behave given who they've shown it to, and show posts more/less widely based on whether it's over/underperforming their prediction.