If you're after pulled pork you need time for the collagen in the butt to convert to gelatin. The does happen as low as 130F but at that temperature the process is very slow. The pullable texture you seek is achievable at 130F, but it would possibly take 4 or 5 days. At higher temperatures the conversion is almost simultaneous.
At 175F you probably wouldn't need 24 hrs, but much depends on the dimensions of the piece of meat. I'm sure there is something in the forum archive that discusses the best time and temperature for your desired outcome.
As has already been pointed out, fat won't render at sous vide temperatures. Many folk will sous vide to cook the meat and then smoke for flavour and finish.