I don't know why you would wait to add fo at all. The hottest you need to any vegetable wax is 180. And that would be just to add uv inhibitors, some addatives or powdered dyes. If you add 4 oz of fo to a 4 lb batch, you will lose 10 degrees or so. Stirring will further lower the temp. Mostly heating to about 165 is enough. You need to add fo at at least 150 degrees for proper blending. HTH