I'm not sure that shade map is so accurate. I looked at my house and it wasn't even close. Also, it completely changed based on zoom level. If you zoom in it will show tall buildings shading all day, but I assure you that the tall buildings nearby do not provide any shade to my property.
It's a bit tricky with high zoom levels because there might be a mountain 5 miles away that's casting shade on your block but at high zoom levels, features far away tend to be ignored for performance reasons.
I've been using the map for mountaineering and in my experience it's quite accurate +/-2 to 3 minutes.
Do you live in the extreme north or south? Maybe the elevation data for your region is not accurate. The buildings are not quite fleshed out yet. Here's another project that might provide better results: https://app.shadowmap.org
I live in Cupertino, right between the two Apple campuses. The problem for me is too much shadow. For example, it says that the Apple campuses keep my house in shadow for much of the day, which I can assure you is not accurate. Other tall buildings cause the same problem.
It probably works a lot better in nature where all of the sources of shadow are natural mountains.
