In my experience, all these formal 20% things are just too artificial, and usually just marketing. The only important thing (but also the most challenging) is t

In my experience, all these formal 20% things are just too artificial, and usually just marketing. The only important thing (but also the most challenging) is to ensure that there is enough slack in the schedule. If you can manage that, well, you've got a bunch of hackers with some hardware, an internet connection and time on their hands. The rest will pretty much sort itself out.