In the USA it happens as you pass the sign, and the impact is quite quick. However, perhaps you should raise a localization bug with Tesla that "down speed changes" should complete by the time you get to the sign.
Seems like the Boombox feature is limited to North American vehicles only. Mine is a bit too old for the speaker (it's a pre-Sep 2019 build) but even cars from the last delivery batch appear to be missing the feature. I wonder if there are laws here that prevent it?
Having driven now with the new update a few times, there are a few things I am not liking. I don't like the reduced map size, the Hold symbol is hidden by your hand on the steering wheel. Initially I thought it was missing but the function was still working and then found the symbol low down on the right of the screen. The P N R D symbols are way too light and difficult to see. I do like the turn signals where they are though.I think there will be some changes in new updates soon.
I agree, the reduced map size makes no sense to me and is very disappointing. The visualisation area is now just too large with most often just empty space. New car angle looks nice but takes up more space and has same ability to open frunk/trunk/charge port. I don't mind the symbols down the side but agree PRND is now too light. Finally, speed font is smaller and I don't like that. This is the first update since I got my car (about 25 updates ago) that feels half-baked and is disappointing. There's really nothing new other than messing up the U/I... minor change to scheduled departure and a couple games. My 2 cents for what it's worth.
Noticed today that the nav directions appear on the visualisation side when your passenger is fiddling with the music and blocking the map side. I do like that.