Improve flexibility and wellness
Slowly roll your neck in circles
Short stretches you can do beside a desk without changing clothes, aimed at the stiffness that accumulates through a working day.
The problem with desk work is not posture so much as stillness. Holding any position for hours is what causes discomfort, which is why moving regularly matters more than sitting perfectly.
These are general wellbeing exercises, not medical advice. If you have a health condition, are recovering from injury, or find that an exercise causes pain rather than mild discomfort, speak to a qualified professional rather than working through it.
Twenty to thirty seconds for static stretches. Shorter holds produce little benefit, and bouncing into a stretch increases injury risk without improving flexibility.
Briefly every hour or so is more useful than one long session. The underlying problem is staying still, so frequency matters more than duration.
No. Aim for mild tension. Sharp or increasing pain means you have gone too far and should ease off.