You should sit on your yoga ball chair for about one to two hours a day. This is just enough time to break the monotony of sitting in a classic desk chair without overdoing it. If you stick with the yoga ball for your entire workday, your back might just end up suffering instead of feeling better. This is because yoga balls lack the structure to stop you from slumping once your body starts to get tired. So, unless you’re super disciplined regarding posture, it’s best to pick just a couple of hours to bounce.