No companies should be offering 20% time anyway because it's a difficult promise to keep between crunch schedules and need to keep work between teams synchronized. Some companies also have creative interpretations of "20% time" as "We offer 20% time: you can spend 20% of your time doing whatever marketing needs you to do" turning the whole notion of 20% time into a disincentive.
Hack Days work much better. Easier to accommodate and more fun.
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