Perhaps these books are referring to hours on Venus, which last ten Earth days. So twenty four hours is around 224.7 Earth days. You could get a pretty good grasp of ASP.NET in 224.7 earth days assuming around the clock reading and studying.
I personally like the HeadFirst series. They don’t attempt to dumb it down too much, but do realize that people learn better when the writing does not put them to sleep. Osmosis is no way to learn.