You're right, the duration language is my fault, I'll change that. You haven't heard of timehashes because I invented them 😉
It's actually not too bad to either publish or query these, since if all three recommended levels of granularity exist as tags you can choose which to target with a filter depending on how wide your window is. The degenerate edge case is of course events that last for a long time, since you have to enumerate approximately every hour. I'm not quite sure what to do in that situation.