It looks like the mouse lines and the selection highlight are just partially-transparent divs stacked on top of the canvas that get moved around, so nothing actually gets redrawn unless the date range changes (which is a pretty clever approach!).
The selection highlight is unusual, I admit. That's something I'd just skip if I were going for high performance.
no, the top graph is pretty much what the title says: 3 * 365 * 24.
but 194k is also no problem :)