From The Food Lab’s Guide to Sous Vide Ribs
"For my recipe, I tested combinations of temperatures ranging from as low as 140°F (60°C) to as high as 180°F (82°C), with timings ranging from 4 hours and up to 48. Unsurprisingly, I found that the lower the temperature, the longer it takes for tough connective tissue to soften, and the more moisture the meat retains. Ribs cooked at a higher temperature have a more traditional texture than those cooked at a lower temperature, but both have their advantages. For extra meaty, succulent and tender ribs: I like giving my ribs a good rub with a homemade spice blend, letting them rest for 4 to 12 hours to allow the salt to penetrate the meat, then cooking them at 145°F (63°C) for 36 hours for an extra-meaty bite. For tender, traditional BBQ ribs: At a higher temperature, you can recreate the classic, backyard BBQ rib texture with well-rendered fat and meat that shreds as you eat it. To get this style, I cooked the ribs at 165°F (74°C) for 12 hours which resulted in a traditionally tender, slightly shreddy texture that pulls easily from the bone with just the slightest bit of resistance.
 
 And what about that smoke? Well you could start or finish the ribs on a smoker to get that smoker flavor into them, but then you reintroduce that unpredictable element. It’s much easier and more consistent to simply use a few drops of liquid smoke added directly to the sous vide bags before sealing. A good quality liquid smoke like Wright’s or Colgin are nothing more than wood smoke that has been condensed and captured in water and stuck in a bottle. It’s literally the exact same stuff that gets deposited on your meat when you smoke it in a smoker, and there’s no reason to shun it or be afraid of it. I finish my ribs by either cooking them over moderate heat on a grill, or set on a rack in the oven. If I’m adding a sauce, I’ll paint it on in a few layers towards the end of cooking to get a nice, thickly reduced coat of it.
 The only thing missing from sous-vide ribs is that pink smoke ring, which is a purely cosmetic detail. It offers no flavor or textural differences in traditional barbecue. If you must have that pink ring, adding pink curing salt to the rub before applying it to the pork will help set its color. Use about 2 grams of pink salt for every kilogram of pork (about .03 ounces per pound)."

145° for 36 hours.
155° for 24 hours.
165° for 12 hours.