[wtracy]

I've never ever heard of that actually becoming a requirement.

What happens is that some managers really don't buy into the 20% concept, and don't provide time for it. Employees in those teams determined to do it anyway end up doing 120%.

There is absolutely no requirement at Google to put in time on a 20% project.

That said, what happens in practice is that 20% projects are the way that Google engineers are able to move across teams: You pick a team you want to join. You do something for that team as your 20% project with the goal of getting that manager to request your transfer to their team.

So if you're desperate to get off your team without quitting Google, you could get backed into committing 120%.