There are a number of example date functions and workbooks that are found here: Calculation Reference Library
Let us know if one of these gets you going and if you get stuck, let us know where to help provide a bit more insight.
I decided that given the size of the data I was working with and the accuracy needed on the means I would be calculating against, the best way was to create a separate data source that I summarized from a 90+ day time sample.
This Viz relies on speed and performance for the end users, so no time to waste computing nested calcs like that.
So with some guidance I created a table grouped on each class and an hour segment of the day, then published that sum table in the same workflow currently automated.
The CORRECT ANSWER FOR THE ISSUE: was to create a table calculation finding the means by class and by hour which I did, what I DID NOT DO was remember to alter the date and time filters used for each page, as the mean-tables were being applied on each page of the workbook.
If the user moved the date range to a day, or the last 2 hours, the mean tables were moving to that same time.
DUH...An obvious error but a good reminder to pay close attention to the filer details when building these kinds of dashboards.