How long does it take to slow roast a 13 pound bone-in fresh ham? We want to bring it to 190 degrees F to break down the collagen.
There is no single answer to this question.
Even saying you want to bring it to a temperature of 190 (I infer F) is overly simplified, as the conversion of collagen to gelatin is dependent on both time and temperature. It goes faster at higher temperatures, but still takes time. There is no single magic temperature that when you hit it, the conversion is done.
The time it takes to cook the fresh ham will depend on the size of the ham, the method you use to cook the ham (for example, braising versus dry roasting, and the oven temperature you set.
The time will also depend on whether you want to be able to pull the pork (although should is somewhat better suited to that application), or carve it into slices.
Roasting at 225 F, 10-14 hours would not be out of the question. At 325 F, it may take 6-9 hours. Start checking for donenesss at the beginning of the time.
The ham will be done when you can put a fork in it and twist without too much resistance, demonstrating that it is pullable.