Break send into smaller batches over 1 hour/day -- what's the breakdown?

When using the "Break send into smaller batches" feature for multiple days or hours, the smaller batches usually go out at the top of the hour or day.. But what happens when you set the sending period to 1 hour, or 1 day… does it break the batch over that hour or day? and how many batches does it break into?

I'm running some tests but if someone can share what they've studied before, that would either verify or contradict my research..