What is the adaptive repost interval?
Every day, that Friends+Me does not fetch any new posts, your account repost interval will slow down. But it will be immediately restored to the fastest possible interval with the first repost. These rules are applied for every single Google+ account separately.
What is it all about? Well, if you publish at least one post a day, you will always have the fastest possible repost interval. The repost interval will be reduced only for accounts with irregular publishing.
A day without any repost? From the start till the end of the day you do not repost any published post.