What temp are you cooking them on? Try 180C for 30-35 minutes... leaving them without anything covering them will give you the crispy skins still. I cooked some last night and 30min left them a little pink so another 5-10 min would have been good (but I wanted them not fully cooked as DH microwavs them at work). It really depends on the size. But I think the temp is the biggest thing...