Forty minutes. Parboil, rough up the edges, then roast hard in fat with whole rosemary sprigs tucked underneath.
The rule that matters: woody herbs go in at the start, soft herbs at the end. Rosemary, thyme and bay can take the heat and need it to release their oil. Basil, coriander and chives cannot, and will taste of nothing if you cook them.
Pull the sprigs before serving. They have done their work.