This was implemented! Thank you

Workaround 1: in the Day view timeline you can select an existing tag, press Ctrl+C to copy it, then press Ctrl+V to tag the currently selected time with those exact same Tag and Notes.

Workaround 2: when you select time, the little "amount of time" box which appears when you release the mouse has a big white-on-blue arrow. Clicking the arrow will open a menu with the most recently used tags at the top, which you can then pick with a single click without having to open the "Add tag" window, saving some clicks / key presses.

Would love to see a shortcut that tags the selected block of time with the last tag used, i.e. the tag that's at the top of the "add tag" list.

I often go through my timeline to find the spots throughout the day where I was working on a particular project, and I tag each of these blocks of time as I go through. Instead of having to open the "add tag" window every time (press Ctrl+T, then click on the tag at the top of the list to copy it and the notes over to the left, then press Ctrl+Enter to select it and close the window) it would be great to simply press a keyboard shortcut, like we can do with tag shortcuts. In this case, though, I can't use a tag shortcut because there's just too many possible tags/note combinations that I might want to use over the span of a week or two.

Another way to think of this request: it's a tag shortcut, but the actual tag and note aren't static -- they are always based on the last tag and note you assigned to a block of time. Every time I assign a different tag/note to a block, this "dynamic" tag shortcut changes to reflect this new tag and note combination.