I guess that depends on your interpretation of "calendar". The concept "hour of day" doesn't make sense unless you define a "day" and a reference time. And those things are supplied by a calendar. Note how the unit for a time coordinate is defined as "hours since <a date as written in a calendar>".

Anyway, I guess either we document what exists right now: "Selection by hour-of-day within time coordinates." Or we document what will exist in the future, as it currently does. I'm not fussed which, so you choose. :wink: