Apparently, there's no _true_ offset for extended hours of sitting[1]. There might be some science/studies behind smart watches urging you to stand for a couple of minutes every hour, however.
Depends on how much you care and how able you are to compel yourself into action.
Almost every one of us reading this is in a position to abbreviate our work with physical activity at the very least. I just wager that most of us are too addicted to comfort to actually do anything about it in the face of the evidence. For example, we already know that a sedentary lifestyle is bad yet most people don't exercise.
[1] https://www.theatlantic.com/health/archive/2016/08/the-new-e...