Our team estimates 50% overhead: in other words 8 hours at work = 4 hours of productivity, given meetings, randomizations, etc.
If we didn't have meetings-free focus-Thursday, it would be much worse.
I had two weeks were I was on another team and got to skip all meetings. OMG it was so productive. Unfortunately, that's not sustainable either.
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We strive for transparency and don't collect excess data.