While every oven is different, standard convection oven cooking times tend to be 25 percent less than standard oven cooking times. Alternatively, the cooking temperature could be reduced by 25 percent. Yet another option would be to reduce both the temperature and the time by less than 25 percent.
Standard conventional oven cooking directions for cookies are 350F for 12 minutes. For baked potatoes, cook at 400F for 45 minutes. For 12 pounds of turkey, bake at 325F for 3.5 hours. You should experiment by starting with these conventional cook times and making adjustments for your convection oven. Checking food a little before it is set to be done and being prepared for a period of trial and error is part of this learning process.