Depending on your personal choice and capability, you could spend any amount of time on the hanging bars. With practice, you will be able to stay 30 seconds at a stretch. 3 or 4 minutes every day will be enough to grow taller. Too much hanging could affect your ligaments and muscles and strain them too much. So, refrain from it.
These small tips about hanging will surely make you want to give it a try. Other than hanging, there are other exercises too, that can help you grow taller. Check out a few of them