Why "top of the hour" is not available on any of the apps for Lemmy?

I believe they just added TopHour, TopSixHour, TopTwelveHour in version 0.18 but I don’t think they are implemented yet, because I have not been able to get them to work properly while testing in my app.

It’s not a feature of Lemmy and, I guess, no-one has wanted to create it for their app. You should submit this idea to the Lemmy developers so it will eventually be a feature in every app.