I found an article from the ergonomics section of the Cornell University about sitting and standing at work in front of a computer. It repeats the dangers of sitting for a prolonged time, but it also warns against excessive standing, which is more tiring and can bring its own set of problems.
Instead, this is what is recommended:
- Sit to do computer work. Sit using a height-adjustable, downward titling keyboard tray for the best work posture.
- Every 20 minutes, stand for 8 minutes and move for 2 minutes.
The absolute time sitting or standing isn’t critical, but you should take a posture and movement break every 20-30 minutes. The movement can be lightweight—no need to hit the gym every half an hour; walking will suffice.
Check out the article for more context and the references.