From what I can tell, the Hourly Breakdown is inaccurate because it ignores time zones. For example, mine shows that I’ve answered most of my questions at 2am, but that was when I was answering g questions at 2pm in a time zone 12 hours different from where I am now. I think that graph would be more useful if it was synched to whatever time zone I’m in at the moment.
This is a known issue, and not easy to change I’m afraid.
Ah well, I can live with it. But doesn’t Anki know what time zone I’m in? It doesn’t seem like it should be hard to fix.