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The CEO of Dropbox has a 90/10 rule for remote work
(www.businessinsider.com)
This is a most excellent place for technology news and articles.
A quarter has 13 weeks, so if you do 2 week sprints and align them to start with a quarter, there is 1 week per quarter that is not accounted for. That week can be used for stuff outside of daily activities. It can be used for training, offsites, working on a pet project, etc. Its a good way to build time in the schedule for this type of thing. These types of breaks have tremendous long term value.