It really depends on the school and program, but if you're vigilant you can get through most in 6-7 years.
It's a pretty good deal, really, but you give up a lot on both sides to make it work (summer employment, proper TA'ing, free time to work on your dissertation).
I'd really make sure you want/need both before taking both on. Perhaps start with grad school, and see how that works out first?
Well that is what is at the heart of it all...I can't decide which one I want to do so I figure I would attempt both. I really need to explore what practicing law is like compared to what I see on tv or what people keep telling me (You would be such a great attorney). Being a professor may not be the awesome life I'd assume either. I wish they had forums like this to explore graudate schools for political science.