To convert conventional oven times to convection times, simply lower the temperature by 25 degrees and reduce the cooking time by about 25 percent.Cook in an efficient convection oven with help from a professional chef in this free video on cooking techniques.Expert: Michelle Karam.ploaded on Sep 17, 2010. To convert conventional oven times to convection times, simply lower the temperature by 25 degrees and reduce the cooking time by about 25 percent. Cook in an efficient convection oven with help from a professional chef in this free video on cooking techniques. Expert: Michelle Karam.