Trystan Lea is generally the creator of all things emonCMS, I’m really an electrical engineer who’s been “into” software for a long time (like pre-Apple ][ ). I know a 3rd party graph module is used for emonCMS, but I can’t remember which, otherwise I’d point you towards that.
The only documentation that might help is in the Guides, and that really only covers the basics.
I think the problem you’ve got is very similar to the one here: How to accumulate watt Hours correctly from an input?
but in that case the user is trying to create or log quarter-hourly data from and alongside a 5 s feed. I don’t think the system was designed with that in mind, and it’s proving hard to convince it to do what they want. (You see, generally, we get data at 10 s intervals, so everything revolves around that sort of time interval - seconds and minutes rather than minutes and hours.)