How to hide elements in the hours row?

This looks like the minute part which is included in the standard view. However, it doesn't display if you use timeHeaderCellDuration value other than 60.

I recommend checking the onBeforeTimeHeaderRender event handler - see how you set the HTML.

This seems to work fine:

onBeforeTimeHeaderRender: args => {
    args.header.html = args.header.time.toString("h:mm");
},