Preheat the oven to 300°F. Place the spiral ham cut-side down on a rack in a roasting pan. Cover tightly with foil and bake for 12–15 minutes per pound.
While the ham cooks, add butter, maple syrup, brown sugar, dried cranberries, orange marmalade, and thyme to a saucepan over medium heat. Stir until the butter melts and the mixture is fully combined.
Bring the glaze just to a gentle boil, then reduce to a simmer and cook for 5 minutes, stirring occasionally, until thickened and glossy. Remove from heat and discard thyme sprigs.
About 30 minutes before the ham is done, remove it from the oven and increase the oven temperature to 350°F. Uncover the ham and spoon or brush the glaze generously over the entire surface, letting it drip into the slices.
Return the ham to the oven, uncovered, and bake for the remaining 30 minutes, basting once or twice if desired, until the glaze is sticky and caramelized.
Remove from oven and let rest for 10 minutes before serving.