I've heard from several current Google employees that the so-called "20% time" is known in the office as "120% time". Meaning you don't get time to work on it,

I've heard from several current Google employees that the so-called "20% time" is known in the office as "120% time". Meaning you don't get time to work on it, you simply work on something on top of what you already do. Which actually defeats the purpose and just gets employees to use their personal free time to work on a company project. Nonetheless, it's a good idea for a class, as long as you make sure to give them 20% of class time to work on it