Time and temperature for converting collagen to gelatin in chuck roast cooked sous vide?

This depends on the end result you are looking for. At some point, if you leave it in the bath too long, the texture will probably go too mushy for most peoples' liking, but here are a few observations: Baldwin states that 131F (55C) is the lowest temperature for collagen conversion, and that at higher temperatures the denaturing happens more quickly. So, you could increase the temperature. Since you cooked at 55C, you probably want it on the pink side. You could go as high as 57C or 58C (though now we are getting into "medium" territory) and still have pink meat. Chefsteps has a recipe for chuck roast, and provides a time and temperature guide. They cook for 18 hours with temperatures ranging (depending on your desired outcome) from 54 - 72C (129-162F). I am guessing that 18-24 hours produces something that resembles a more traditional roast in the end. If you are looking for a softer texture, I would go slightly higher on the temperature, and longer on the cook, maybe even 48 hours.

Since asking the question, I came across this paper by Douglas Baldwin: Sous vide cooking: A review which is as close to a chart that I've found. It goes into a bit more detail than the his site.

When cooking tough meats, the dissolving of collagen into gelatin and the reduction of inter-fiber adhesion is important and this takes either a long time or high temperatures. Prolonged cooking (e.g., braising) has been used to make tough cuts of meat more palatable since ancient times. Indeed, prolonged cooking can more than double the tenderness of the meat by dissolving all the collagen into gelatin and reducing inter-fiber adhesion to essentially nothing (Davey et al., 1976). At 80 °C/176 °F, Davey et al. (1976) found that these effects occur within about 12–24 h with tenderness increasing only slightly when cooked for 50–100 h.

At lower temperatures (50 °C/120 °F to 65 °C/150 °F), Bouton and Harris (1981) found that tough cuts of beef (from animals 0–4 years old) were the most tender when cooked to between 55 °C/131 °F and 60 °C/140 °F. Cooking the beef for 24 h at these temperatures significantly increased its tenderness (with shear forces decreasing 26–72% compared to 1 h of cooking). This tenderizing is caused by weakening of connective tissue and proteolytic enzymes decreasing myofibrillar tensile strength. Indeed, collagen begins to dissolve into gelatin above about 55 °F/131 °F (This, 2006). Moreover, the sarcoplasmic protein enzyme collagenase remains active below 60 °C/140 °F and can significantly tenderize the meat if held for more than 6 h (Tornberg, 2005).

For example, tough cuts of meat, like beef chuck and pork shoulder, take 10–12 h at 80 °C/175 °F or 1–2 days at 55–60 °C/130–140 °F to become fork-tender. Intermediate cuts of meat, like beef sirloin, only need 6–8 h at 55–60 °C/130–140 °F to become fork-tender because the tenderization from the enzyme collagenase is sufficient.

So, next time, I will try 135 F (to stay below the 140 F temp mentioned in the last paragraph) since my previous attempt with 131 F was just too slow.