It takes about an hour for a single simple icon, longer for the more complex ones with a lot of moving parts. I isolate a bunch of shapes from the original icon design and stack them up with individual movements to get the cutouts and motions that I need - sometimes I can cleverly reuse some already-made parts of existing animations, but not usually.
I avoid problems with blurriness by being very careful about the image resolutions I upload, but beyond that, I mostly avoid spritesheets just because they tend to have a lower refresh rate than the display.