I would recommend asking your boss to get a desk that you can adjust height for sitting/standing. That way you can stand up while working which is very healthy. You should at least stand one hour per day. I try to do that :)

Jakob Lind has the right idea, I try to stand for about 4 hours for every 12-16 hours of work I do per day. Since I already have a desk, I got a Varidesk which fits on top of my regular desk. (varidesk.com)

A person simply shouldn't sit for any period of 8 hours. That's asking for all sorts of health problems. One should get up regularly and stretch, walk around, get some water, and generally take a deep breath or three. Our bodies need that, they really weren't designed to be sitting for 8 hours, or doing a single activity of any sort for 8 hours. It's really bad for one's health to do something like that over and over. :)