I wouldn't mind those kinds of book titles so much if they just said "Learn basic [language] syntax in [n] [units of time]". Not as catchy I guess, though.
Someone forgot "Perfect doppleganger technology, then go back in time to kill Stroustrup, replace him, and write C++ in a way that you actually can learn it in 21 days. Also, obsolete Sun Microsystems."
I think everyone is taking the title a little too literally. The "24 hours" gimmick is just a way of constraining the information into discrete concepts. Once you know 24 facets of a language, you are certainly qualified to start testing out the language. Is there anyone who really thinks that by reading any number of books on a topic you could consider yourself an expert?
It's doubly funny when you look at the difference between "use knowledge to make an age-reversing <i>potion</i>" which follows with "use knowledge to build flux capacitor"